Group-III nitride semiconductor laser device, method of fabricating group-III nitride semiconductor laser device, and method of estimating damage from formation of scribe groove

ABSTRACT

A method of fabricating group-III nitride semiconductor laser device includes: preparing a substrate comprising a hexagonal group-III nitride semiconductor and having a semipolar principal surface; forming a substrate product having a laser structure, an anode electrode, and a cathode electrode, where the laser structure includes a semiconductor region and the substrate, where the semiconductor region is formed on the semipolar principal surface; scribing a first surface of the substrate product in a direction of an a-axis of the hexagonal group-III nitride semiconductor to form first and second scribed grooves; and carrying out breakup of the substrate product by press against a second surface of the substrate product, to form another substrate product and a laser bar.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.12/837,209, filed Jul. 15, 2010, which claims the benefit of JapanPatent Application No. 2010-002223, filed Jan. 7, 2010, all of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a group-III nitride (referred to asIII-nitride) semiconductor laser device, a method of fabricating theIII-nitride semiconductor laser device, and a method of estimatingdamage from formation of a scribe groove.

2. Related Background Art

Patent Literature 1 describes a laser device. When a principal surfaceof a substrate is a face tilting at 28.1° from a {0001} plane toward adirection equivalent to the [1-100] direction, secondary cleaved facetsare {11-20} planes perpendicular to both of the principal surface andoptical cavity faces, and the laser device is of a rectangularparallelepiped shape.

Patent Literature 2 describes a nitride semiconductor device. The backsurface of the substrate for cleavage is polished to reduce the totallayer thickness to about 100 μm. A dielectric multilayer film isdeposited on cleaved facets.

Patent Literature 3 describes a nitride-based compound semiconductordevice. The substrate used for the nitride-based compound semiconductordevice comprises a nitride-based compound semiconductor with thethreading dislocation density of not more than 3×10⁶ cm⁻² and thein-plane threading dislocation density is substantially uniform.

Patent Literature 4 describes a nitride-based semiconductor laserdevice. In the nitride-based semiconductor laser device, cleaved facetsare formed as described below. With respect to recesses which are madeby etching from a semiconductor laser device layer to an n-type GaNsubstrate, scribed grooves are formed like a dashed line (at intervalsof about 40 μm) in a direction orthogonal to an extending direction ofridge portions, using a laser scriber, while avoiding projections madeduring the etching of cavity faces on the n-type GaN substrate. Then thewafer is cleaved at positions of the scribed grooves. On this occasion,each of regions without the scribed grooves, e.g., each projection, iscleaved from the adjacent scribed groove as an origin. As a result, eachdevice separation face is formed as a cleaved facet consisting of a(0001) plane of the n-type GaN substrate.

Patent Literature 5 describes a light emitting device. The lightemitting device is able to readily emit light at a long wavelength,without deterioration of luminous efficiency in its light emittinglayer.

Patent Literature 6 describes a semiconductor laser. In thissemiconductor laser, cleavage introduction level-differences forcleavage having the depth of about 20 μm are formed from the top side ofa GaN-based semiconductor laser chip in an n-type GaN substrate, asemiconductor layer, and a current block layer. These cleavageintroduction level-differences are spaced by the length of the cavity ofthe semiconductor laser. These cleavage introduction level-differencesare formed only in a region opposite to one side of a ridge part. Thedistance between the cleavage introduction level-differences and theridge part (optical waveguide) is not less than about 70 μm. Thecleavage introduction level-differences are formed in a directionorthogonal to the ridge part 12 a (optical waveguide).

Non-patent Literature 1 describes a semiconductor laser in which awaveguide is provided in an off-axis direction and in which mirrors aremade by reactive ion etching, on a semipolar (10-1-1) plane.

-   Patent Literature 1: Japanese Patent Application Laid-open No.    2001-230497-   Patent Literature 2: Japanese Patent Application Laid-open No.    2005-353690-   Patent Literature 3: Japanese Patent Application Laid-open No.    2007-184353-   Patent Literature 4: Japanese Patent Application Laid-open No.    2009-081336-   Patent Literature 5: Japanese Patent Application Laid-open No.    2008-235804-   Patent Literature 6: Japanese Patent Application Laid-open No.    2008-060555-   Non-patent Literature 1: Jpn. J. Appl. Phys. Vol. 46 (2007) L444

SUMMARY OF THE INVENTION

In the band structure of a GaN-based semiconductor there are sometransitions capable of laser oscillation. According to Inventor'sknowledge, it is considered that in the III-nitride semiconductor laserdevice using the semipolar-plane support base the c-axis of which tiltstoward the m-axis, the threshold current can be lowered when the laserwaveguide extends along a plane defined by the c-axis and the m-axis.When the laser waveguide extends in this orientation, a mode with thesmallest transition energy (difference between conduction band energyand valence band energy) among the possible transitions becomes capableof laser oscillation; when this mode becomes capable of laseroscillation, the threshold current can be reduced.

However, this orientation of the laser waveguide does not allow use ofthe conventional cleaved facets such as c-planes, a-planes, or m-planesfor the cavity mirrors. For this reason, the cavity mirrors have beenmade heretofore by forming dry-etched facets of semiconductor layers byreactive ion etching (RIE). There are now desires for improvement in thecavity mirrors formed by RIE, in terms of perpendicularity to the laserwaveguide, flatness of the dry-etched facets, or ion damage. It becomesa heavy burden to derive process conditions for obtaining gooddry-etched facets in the current technical level.

As far as the inventor knows, no one has succeeded heretofore inachieving both of the laser waveguide extending in the tilt direction(off-axis direction) of the c-axis and the end faces for cavity mirrorsformed without use of dry etching, in the III-nitride semiconductorlaser device formed on the semipolar plane.

Patent Literature 6 describes the formation of scribed grooves forcleavage and the minimum distance between the scribed grooves and theridge part is 70 μm. On the other hand, in the case of a semiconductorlaser made on a semipolar plane of a substrate tilting from the c-axistoward the m-axis of a hexagonal III-nitride as in the presentapplication, the end faces for the cavity cannot be produced by makinguse of cleavage. This semiconductor laser is required to have the lasercavity enabling a low threshold current and is also required to reducethe chip width without significant damage to the laser stripe in formingthe laser cavity. The applicant of the present application filed aJapanese patent application (Japanese Patent Application No.2009-144442) associated with the III-nitride semiconductor laser deviceincluding fractured faces for the optical cavity.

The present invention has been accomplished in view of theabove-described circumstances. It is an object of the present inventionto provide a III-nitride semiconductor laser device with a laser cavityenabling a low threshold current and a structure of ends enablingreduction in chip width at device ends for the laser cavity, on asemipolar plane of a support base tilting from the c-axis toward them-axis of a hexagonal III-nitride and to provide a method forfabricating the III-nitride semiconductor laser device. It is a furtherobject of the present invention to provide a method for estimatingdamage from formation of a scribe groove in a semiconductor laserdevice.

A III-nitride semiconductor laser device according to an aspect of thepresent invention comprises: (a) a laser structure including a supportbase comprising a hexagonal III-nitride semiconductor and having asemipolar principal surface, and a semiconductor region provided on thesemipolar principal surface of the support base; and (b) an electrodeprovided on the semiconductor region of the laser structure. Thesemiconductor region includes a first cladding layer comprising a firstconductivity type gallium nitride (GaN)-based semiconductor, a secondcladding layer comprising a second conductivity type GaN-basedsemiconductor, and an active layer provided between the first claddinglayer and the second cladding layer; the first cladding layer, thesecond cladding layer, and the active layer are arranged along a normalaxis to the semipolar principal surface; the active layer comprises aGaN-based semiconductor layer; the c-axis of the hexagonal III-nitridesemiconductor of the support base tilts at a finite angle ALPHA withrespect to the normal axis toward the m-axis of the hexagonalIII-nitride semiconductor; the laser structure comprises first andsecond fractured faces intersecting with an m-n plane defined by them-axis of the hexagonal III-nitride semiconductor and the normal axis; alaser cavity of the III-nitride semiconductor laser device includes thefirst and second fractured faces; the laser structure includes first andsecond surfaces, and the first surface is a surface opposite to thesecond surface; each of the first and second fractured faces extendsfrom an edge of the first surface to an edge of the second surface.

In the III-nitride semiconductor laser device, the angle between thenormal axis and the c-axis of the hexagonal III-nitride semiconductorcan be in a range of not less than 45° and not more than 80° or in arange of not less than 100° and not more than 135°.

Furthermore, the semiconductor region is located between the firstsurface and the substrate, and the laser structure includes a laserstripe extending in a direction of a waveguide axis above the semipolarprincipal surface of the support base. The waveguide axis extends fromone to the other of the first and second fractured faces. The laserstructure has first and second recesses provided each at a portion ofthe edge of the first surface in the first fractured face. The first andsecond recesses extend from the first surface of the laser structure.Bottom ends of the first and second recesses are located apart from theedge of the second surface of the laser structure. The first recess hasan end at the first surface, and the second recess has an end at thefirst surface. A first distance between the laser stripe and the end ofthe first recess is smaller than a second distance between the laserstripe and the end of the second recess.

In this III-nitride semiconductor laser device, when the angle is in arange of less than 45° or in a range of more than 135°, end faces madeby press are highly likely to be comprised of m-planes. When the angleis in a range of more than 80° and less than 100°, it might result infailing to achieve desired flatness and perpendicularity. Since thefirst distance between the laser stripe and the end of the first recesscan be made smaller than the second distance between the laser stripeand the end of the second recess, the device width, of the laser devicecan be reduced.

In this III-nitride semiconductor laser device, because the first andsecond fractured faces to form the laser cavity intersect with the m-nplane defined by the m-axis of the hexagonal III-nitride semiconductorand the normal axis, it is feasible to provide the laser waveguideextending in a direction of an intersecting line between the m-n planeand the semipolar plane. Therefore, the present invention succeeds inproviding the III-nitride semiconductor laser device with the lasercavity enabling a low threshold current.

In the III-nitride semiconductor laser device according to the presentinvention, the first and second recesses can be provided along apredetermined plane defined by the a-axis of the hexagonal III-nitridesemiconductor and the normal axis. In this III-nitride semiconductorlaser device, each of the first and second recesses includes a scribedmark formed from a scribed groove by fracture. The scribed groove guidesprogress of the fracture, and is divided during the fracture to form thescribed mark in each laser bar. The first and second recesses areprovided along the predetermined plane (referred to as “a-n plane”).

A III-nitride semiconductor laser device according to an aspect of thepresent invention comprises: (a) a laser structure including a supportbase and a semiconductor region, the support base comprising a hexagonalIII-nitride semiconductor and having a semipolar principal surface and aback surface, the semiconductor region being provided on the semipolarprincipal surface of the support base; and (b) an electrode provided onthe semiconductor region of the laser structure. The semiconductorregion includes a first conductivity type cladding layer, a secondconductivity type cladding layer, and an active layer, the active layerbeing provided between the first cladding layer and the second claddinglayer; the first conductivity type cladding layer, the secondconductivity type cladding layer, and the active layer are arrangedalong a normal axis to the semipolar principal surface; the c-axis ofthe hexagonal III-nitride semiconductor of the support base tilts at anangle ALPHA with respect to the normal axis toward the m-axis of thehexagonal III-nitride semiconductor; the angle ALPHA is in a range ofnot less than 45° and not more than 80° or in a range of not less than100° and not more than 135°; the laser structure includes first andsecond surfaces; the first surface is a surface opposite to the secondsurface; the semiconductor region is located between the first surfaceand the support base; the laser structure has first and second scribedmarks provided at one end and the other end, respectively, of an edge ofthe first surface at an end of the laser structure; the first and secondscribed marks extend along an a-n plane defined by the a-axis of thehexagonal III-nitride semiconductor and the normal axis; the first andsecond scribed marks extend from the first surface; the end of the laserstructure has a fractured face connecting edges of the first and secondscribed marks and edges of the first and second surfaces of the laserstructure; a laser cavity of the III-nitride semiconductor laser deviceincludes the fractured face; the laser structure includes a laser stripeextending in a direction of a waveguide axis above the semipolarprincipal surface of the support base; the first scribed mark has an endat the first surface; the second scribed mark has an end at the firstsurface; a first distance between the laser stripe and the end of thefirst scribed mark is smaller than a second distance between the laserstripe and the end of the second scribed mark.

In this III-nitride semiconductor laser device, when the angle is in arange of less than 45° or in a range of more than 135°, an end faceformed by press is highly likely to be comprised of an m-plane. When theangle is in a range of more than 80° and less than 100°, the desiredflatness and perpendicularity might not be achieved. Each of the firstand second scribed marks is formed from a scribed groove by fracture,and the scribed groove guides progress of the fracture. Furthermore,since the first distance between the laser stripe and the end of thefirst scribed mark can be made smaller than the second distance betweenthe laser stripe and the end of the second scribed mark, the devicewidth of the laser device can be reduced.

In the III-nitride semiconductor laser device according to the presentinvention, the first distance can be not less than 20 μm. In thisIII-nitride semiconductor laser device, the end of the recess can belocated up to the close distance of 20 μm from the laser stripe. Thefirst distance can be less than 50 μm. In this III-nitride semiconductorlaser device, when the first distance is less than 50 μm, it promisescontribution to reduction in device width.

In the III-nitride semiconductor laser device according to the presentinvention, the first distance can be less than 50 μm and the seconddistance can be not less than 50 μm. In this III-nitride semiconductorlaser device, the device width of the laser device can be reducedbecause the first distance can be made smaller than the second distance.

In the III-nitride semiconductor laser device according to the presentinvention, a width of the III-nitride semiconductor laser device can benot more than 200 μm. This III-nitride semiconductor laser device canprovide the device width of not more than 200 μm.

In the III-nitride semiconductor laser device according to the presentinvention, more preferably, the angle between the normal axis and thec-axis of the hexagonal III-nitride semiconductor falls within a rangeof not less than 63° and not more than 80° or within a range of not lessthan 100° and not more than 117°.

In this III-nitride semiconductor laser device, when the angle is in arange of not less than 63° and not more than 80° or in a range of notless than 100° and not more than 117°, end faces made by press arehighly likely to be faces nearly perpendicular to the principal surfaceof the substrate. When the angle is in a range of more than 80° and lessthan 100°, it might result in failing to achieve the desired flatnessand perpendicularity.

In the III-nitride semiconductor laser device according to the presentinvention, a thickness of the support base is preferably not more than400 μm. This III-nitride semiconductor laser device is suitable forobtaining good-quality fractured faces for the laser cavity.

In the III-nitride semiconductor laser device according to the presentinvention, more preferably, a thickness of the support base is not lessthan 50 μm and not more than 100 μm. When the thickness is not less than50 μm, handling becomes easier, and production yield becomes higher.When the thickness is not more than 100 μm, it is more suitable forobtaining good-quality fractured faces for the laser cavity.

In the III-nitride semiconductor laser device according to the presentinvention, laser light from the active layer is polarized in a directionof the a-axis of the hexagonal III-nitride semiconductor. In thisIII-nitride semiconductor laser device, a band transition allowing forachievement of a low threshold current has polarized nature.

In the III-nitride semiconductor laser device according to the presentinvention, light in the LED mode in the III-nitride semiconductor laserdevice includes a polarization component I1 in the direction of thea-axis of the hexagonal III-nitride semiconductor, and a polarizationcomponent I2 in a projected direction of the c-axis of the hexagonalIII-nitride semiconductor on the principal surface, and the polarizationcomponent I1 is greater than the polarization component I2. ThisIII-nitride semiconductor laser device can lase with the laser cavity toemit light in a mode with large emission intensity in the LED mode.

In the III-nitride semiconductor laser device according to the presentinvention, preferably, the semipolar principal surface is one of a{20-21} plane, a {10-11} plane, a {20-2-1} plane, and a {10-1-1} plane.

This III-nitride semiconductor laser device allows for provision offirst and second end faces with flatness and perpendicularity enough toconstruct the laser cavity of the III-nitride semiconductor laserdevice, on these typical semipolar planes.

In the III-nitride semiconductor laser device according to the presentinvention, the semipolar principal surface suitably applicable is asurface with a slight slant in a range of not less than −4° and not morethan +4° from any one semipolar plane of a {20-21} plane, a {10-11}plane, a {20-2-1} plane, and a {10-1-1} plane, toward an m-plane.

This III-nitride semiconductor laser device allows for provision of thefirst and second end faces with flatness and perpendicularity enough toconstruct the laser cavity of the III-nitride semiconductor laserdevice, on the slight slant surface from these typical semipolar planes.

In the III-nitride semiconductor laser device according to the presentinvention, preferably, a stacking fault density of the support base isnot more than 1×10⁴ cm⁻¹.

In this III-nitride semiconductor laser device, because the stackingfault density is not more than 1×10⁴ cm⁻¹, the flatness and/orperpendicularity of the fractured faces is unlikely to be disturbed fora certain accidental reason.

In the III-nitride semiconductor laser device according to the presentinvention, the support base can comprise any one of GaN, AlGaN, AlN,InGaN, and InAlGaN.

In this III-nitride semiconductor laser device, when the substrate usedcomprises one of these GaN-based semiconductors, it becomes feasible toobtain the first and second end faces applicable to the cavity. Use ofan AlN substrate or AlGaN substrate allows for increase in degree ofpolarization and enhancement of optical confinement by virtue of lowrefractive index. Use of an InGaN substrate allows for decrease inlattice mismatch rate between the substrate and the light emitting layerand improvement in crystal quality.

The III-nitride semiconductor laser device according to the presentinvention can further comprise a dielectric multilayer film provided onat least one of the first and second fractured faces.

In this III-nitride semiconductor laser device, an end face coat is alsoapplicable to the fractured faces. The end face coat allows foradjustment of reflectance.

In the III-nitride semiconductor laser device according to the presentinvention, the active layer can include a quantum well structureprovided so as to generate light at a wavelength of not less than 430 nmand not more than 600 nm. Since this III-nitride semiconductor laserdevice makes use of the semipolar plane, the resultant device is theIII-nitride semiconductor laser device making efficient use ofpolarization in the LED mode, and achieves a low threshold current.

In the III-nitride semiconductor laser device according to the presentinvention, more preferably, the active layer includes a quantum wellstructure provided so as to generate light at a wavelength of not lessthan 500 nm and not more than 600 nm. Since this III-nitridesemiconductor laser device makes use of the semipolar plane, it allowsfor increase in quantum efficiency through decrease of the piezoelectricfield and improvement in crystal quality of the light emitting layerregion and it is thus suitably applicable to generation of light at thewavelength of not less than 500 nm and not more than 600 nm.

In the III-nitride semiconductor laser device according to the presentinvention, an end face of the support base and an end face of thesemiconductor region are exposed in each of the first and secondfractured faces, and an angle between the end face of the semiconductorregion in the active layer and a reference plane perpendicular to them-axis of the support base comprising the hexagonal nitridesemiconductor is an angle in a range of not less than (ALPHA−5)° and notmore than (ALPHA+5)° on a first plane defined by the c-axis and them-axis of the III-nitride semiconductor.

This III-nitride semiconductor laser device has the end faces satisfyingthe foregoing perpendicularity, concerning the angle taken from one tothe other of the c-axis and the m-axis.

In the III-nitride semiconductor laser device according to the presentinvention, preferably, the angle is in a range of not less than −5° andnot more than +5° on a second plane perpendicular to the first plane andthe normal axis.

This III-nitride semiconductor laser device has the end faces satisfyingthe foregoing perpendicularity, concerning the angle defined on theplane perpendicular to the normal axis to the semipolar plane.

In the III-nitride semiconductor laser device according to the presentinvention, the electrode extends in a direction of a predetermined axis,and the first and second fractured faces intersect with thepredetermined axis.

In the III-nitride semiconductor laser device according to the presentinvention, the laser structure can further comprise an insulating filmwith an aperture, the insulating film being provided on thesemiconductor region. The electrode is connected through the aperture ofthe insulating film to the semiconductor region of the laser structure.The first distance can be defined by a distance between the aperture ofthe insulating film and the end of the first recess, and the seconddistance can be defined by a distance between the aperture of theinsulating film and the end of the second recess. In this III-nitridesemiconductor laser device, each of the first and second distances isdefined by the distance between the aperture of the insulating film andthe end of the first and second recesses. In the III-nitridesemiconductor laser device according to the present invention, theaperture of the insulating film can have, for example, a stripe shape.

In the III-nitride semiconductor laser device according to the presentinvention, the semiconductor region of the laser structure can have aridge structure. The first distance can be defined by a distance betweenthe ridge structure and the end of the first recess, and the seconddistance can be defined by a distance between the ridge structure andthe end of the second recess. In this III-nitride semiconductor laserdevice, each of the first and second distances is defined by thedistance between the ridge structure and the end of the first and secondrecesses.

In the III-nitride semiconductor laser device according to the presentinvention, preferably, the first recess includes a slope portion wherethe bottom end of the first recess tilts toward the end of the firstrecess; the second recess includes a slope portion where the bottom endof the second recess tilts toward the end of the second recess; a firstlength of the slope portion of the first recess is longer than a secondlength of the slope portion of the second recess. In this III-nitridesemiconductor laser device, the scribed groove is formed so that thefirst length is longer than the second length, whereby it becomesfeasible to reduce an adverse effect on laser operation from damage nearthe end of the first recess with damage greater than damage at the endof the second recess.

Another aspect of the present invention relates to a method forfabricating a III-nitride semiconductor laser device. This methodcomprises: (a) a step of preparing a substrate comprising a hexagonalIII-nitride semiconductor and having a semipolar principal surface; (b)a step of forming a substrate product having a laser structure, an anodeelectrode, and a cathode electrode, the laser structure including asemiconductor region and the substrate, the semiconductor region beingformed on the semipolar principal surface; (c) a step of scribing afirst surface of the substrate product in a direction of the a-axis ofthe hexagonal III-nitride semiconductor to form first and second scribedgrooves; and (d) a step of carrying out breakup of the substrate productby press against a second surface of the substrate product, to formanother substrate product and a laser bar. The first surface is asurface opposite to the second surface; the semiconductor region islocated between the first surface and the substrate; the laser bar hasfirst and second end faces extending from the first surface to thesecond surface and made by the breakup; the first and second end facesform a laser cavity of the III-nitride semiconductor laser device; theanode electrode and the cathode electrode are formed on the laserstructure; the semiconductor region includes a first cladding layercomprising a first conductivity type GaN-based semiconductor, a secondcladding layer comprising a second conductivity type GaN-basedsemiconductor, and an active layer provided between the first claddinglayer and the second cladding layer; the first cladding layer, thesecond cladding layer, and the active layer are arranged along a normalaxis to the semipolar principal surface; the active layer includes aGaN-based semiconductor layer; the c-axis of the hexagonal III-nitridesemiconductor of the substrate tilts at a finite angle ALPHA withrespect to the normal axis toward the m-axis of the hexagonalIII-nitride semiconductor; the first and second end faces intersect withan m-n plane defined by the m-axis of the hexagonal III-nitridesemiconductor and the normal axis. The angle ALPHA is in a range of notless than 45° and not more than 80° or in a range of not less than 100°and not more than 135°.

In this method, the substrate product includes a laser stripe extendingabove the semipolar principal surface; the laser stripe extends in adirection of a waveguide axis; the waveguide axis extends from one tothe other of the first and second end faces; and the first scribedgroove, the laser stripe, and the second scribed groove are arranged inorder in a direction of the a-axis of the hexagonal III-nitridesemiconductor. The first scribed groove has an end at the first surfaceand the second scribed groove has an end at the first surface. A firstdistance between the laser stripe and the end of the first scribedgroove is smaller than a second distance between the laser stripe andthe end of the second scribed groove and a distance between the end ofthe first scribed groove and the end of the second scribed groove issmaller than a width of the III-nitride semiconductor laser device.

According to this method, the first surface of the substrate product isscribed in the direction of the a-axis of the hexagonal III-nitridesemiconductor and thereafter the breakup of the substrate product iscarried out by press against the second surface of the substrateproduct, thereby forming the other substrate product and the laser bar.For this reason, the first and second end faces are formed in the laserbar so as to intersect the m-n plane defined by the m-axis of thehexagonal III-nitride semiconductor and the normal axis. This end faceforming method provides as the first and second end faces, cavity mirrorfaces with flatness and perpendicularity enough to construct the lasercavity of the III-nitride semiconductor laser device, or without iondamage.

In this method, the laser waveguide extends in a direction of tilt ofthe c-axis of the hexagonal III-nitride, and the mirror end faces of thecavity capable of providing this laser waveguide are formed without useof dry-etched facets. In this method, when the angle is in a range ofless than 45° or in a range of more than 135°, the end faces made bypress are highly likely to be comprised of m-planes. When the angle isin a range of more than 80° and less than 100°, it might result infailing to achieve the desired flatness and perpendicularity.

In this method, the scribed grooves and laser stripes can be alternatelyarranged in the a-axis direction on the substrate product. A scribedgroove is formed between two adjacent laser stripes. Damage due toformation of a scribed groove is not isotropic near the scribed groove.Namely, a damaged region due to formation of a scribed groove is formedin asymmetry near the scribed groove. For this reason, the size of thedamaged region near one end of the scribed groove is smaller than thatof the damaged region near the other end of the scribed groove. Whenattention is focused on one laser stripe among the array of laserstripes, the first distance (distance between the laser stripe and theend of the first scribed groove) can be made smaller than the seconddistance (distance between the laser stripe and the end of the secondscribed groove). For this reason, the device width of the laser devicecan be reduced.

In the method according to the present invention, the first distance canbe not less than 20 μm. According to this method, the size of thedamaged region near one end of the scribed groove is smaller than thesize of the damaged region near the other end of the scribed groove onthe substrate product. The end of the scribed groove with the smallersize of the damaged region can be located up to the minimum distance ofabout 20 μm from the laser stripe. In the method according to thepresent invention, the first distance can be less than 50 μm. In thismethod, the end of the scribed groove with the smaller size of thedamaged region can be located up to the close distance of about 50 μmfrom the laser stripe.

In the method according to the present invention, the first distance canbe less than 50 μm and the second distance can be not less than 50 μm.In this method, the adjacent scribed grooves are formed so that thefirst distance is smaller than the second distance, which can reduce thedevice width of the laser device.

In the method according to the present invention, a width of theIII-nitride semiconductor laser device can be not more than 200 μm. Inthis method, the laser device can be formed in the device width of notmore than 200 μm.

In the method according to the present invention, the step of formingthe substrate product comprises performing processing such as slicing orgrinding of the substrate so that a thickness of the substrate becomesnot more than 400 μm, and the second surface can be a processed surfacemade by the processing. Alternatively, it can be a surface including anelectrode formed on the processed surface.

In the method according to the present invention, the step of formingthe substrate product comprises polishing the substrate so that thethickness of the substrate becomes not less than 50 μm and not more than100 μm, and the second surface can be a polished surface formed by thepolishing. Alternatively, it can be a surface including an electrodeformed on the polished surface.

With the substrate in such thickness, it is feasible to form the firstand second end faces with flatness and perpendicularity enough toconstruct the laser cavity of the III-nitride semiconductor laserdevice, or without ion damage, in good yield.

In the method according to the present invention, more preferably, theangle ALPHA can fall within a range of not less than 63° and not morethan 80° or within a range of not less than 100° and not more than 117°.When the angle is in a range of less than 63° or in a range of more than117°, an m-plane can appear in part of an end face made by press. Whenthe angle is in a range of more than 80° and less than 100°, the desiredflatness and perpendicularity are not achieved.

In the method according to the present invention, preferably, thesemipolar principal surface is any one of a {20-21} plane, a {10-11}plane, a {20-2-1} plane, and a {10-1-1} plane.

With these semipolar planes, it is also feasible to provide the firstand second end faces with flatness and perpendicularity enough toconstruct the laser cavity of the III-nitride semiconductor laserdevice, or without ion damage.

In the method according to the present invention, the semipolarprincipal surface suitably applicable is a surface with a slight slantin a range of not less than −4° and not more than +4° from any onesemipolar plane of a {20-21} plane, a {10-11} plane, a {20-2-1} plane,and a {10-1-1} plane, toward the m-plane.

With the slight slant surface from these typical semipolar planes, it isalso feasible to provide the first and second end faces with flatnessand perpendicularity enough to construct the laser cavity of theIII-nitride semiconductor laser device, or without ion damage.

In the method according to the present invention, the scribing iscarried out using a laser scriber, the scribing forms a scribed groove,and a length of the scribed groove is shorter than a length of anintersecting line between an a-n plane defined by the a-axis of thehexagonal III-nitride semiconductor and the normal axis, and the firstsurface.

According to this method, the other substrate product and the laser barare formed by fracture of the substrate product. This fracture isbrought about by using the scribed groove shorter than a fracture lineof the laser bar.

In the method according to the present invention, an end face of theactive layer in each of the first and second end faces can make an anglein a range of not less than (ALPHA−5)° and not more than (ALPHA+5)° on aplane defined by the c-axis and the m-axis of the hexagonal III-nitridesemiconductor, with respect to a reference plane perpendicular to them-axis of the support base comprising the hexagonal nitridesemiconductor.

This method allows for forming the end faces with perpendicularity asmentioned above, as to the angle taken from one to the other of thec-axis and the m-axis.

In the method according to the present invention, the substrate cancomprise any one of GaN, AlN, AlGaN, InGaN, and InAlGaN. This methodallows the first and second end faces applicable to the cavity to beobtained through the use of the substrate comprising one of theseGaN-based semiconductors.

In the method according to the present invention, the laser structurecan further include an insulating film having an aperture and providedon the semiconductor region. The electrode is connected through theaperture of the insulating film to the semiconductor region of the laserstructure; the first distance can be defined by a distance between theaperture of the insulating film and the end of the first scribed groove.In this method, each of the first and second distances is defined by thedistance between the aperture of the insulating film and the end of thefirst and second recesses. The electrode is in contact with thesemiconductor region through the aperture of the insulating film. Thiscontact defines an area where carriers flow from the electrode into thesemiconductor region. The carriers contribute to emission throughrecombination in the active layer.

In the method according to the present invention, the semiconductorregion of the laser structure can have a ridge structure; the firstdistance can be defined by a distance between the ridge structure andthe end of the first scribed groove. In this method, each of the firstand second distances is defined by the distance between the ridgestructure and the end of the first and second recesses. Carriers flowingfrom the electrode into the semiconductor region are guided to the ridgestructure. This ridge structure defines a range where carriers flow fromthe electrode into the semiconductor region. The carriers contribute toemission through recombination in the active layer.

Still another aspect of the present invention is a method of estimatingdamage from formation of a scribe groove. This method comprises: (a) astep of forming a groove in a semiconductor device including a hexagonalIII-nitride semiconductor, using a device for forming a scribed groove;(b) a step of obtaining an image of a region including the groove of thesemiconductor device, using either of a scanning electron microscope anda cathodoluminescence measuring device for the semiconductor device,after formation of the groove; and (c) a step of making an estimation ona level of damage near the groove, based on the image. The semiconductordevice includes a substrate comprising a hexagonal III-nitridesemiconductor and a hexagonal III-nitride semiconductor region formed onthe substrate, or includes a substrate comprising a hexagonalIII-nitride semiconductor.

According to this method, there appears a difference according to thedamage due to the formation of the scribed groove in the image of theregion near the groove, which is obtained with either of the scanningelectron microscope and the cathodoluminescence measuring device. Theestimation on the level of damage near the groove can be made based onthe image obtained with the scanning electron microscope or thecathodoluminescence measuring device.

The method according to the foregoing aspect of the present inventioncan further comprise a step of determining a distance between an end ofthe scribed groove and a laser stripe of a semiconductor laser, based onthe estimation. In this method, the distance between the scribed grooveand the laser stripe can be determined based on the estimating damagefrom formation of the scribe groove.

A further aspect of the present invention relates to a method forfabricating a III-nitride semiconductor laser device. This methodcomprises: (a) a step of forming a groove in a semiconductor deviceincluding a hexagonal III-nitride semiconductor, using a device forformation of a scribed groove; (b) a step of obtaining an image of aregion including the groove of the semiconductor device, using either ofa scanning electron microscope and a cathodoluminescence measuringdevice for the semiconductor device, after formation of the groove; (c)a step of making an estimation on a level of damage near the groove,based on the image; (d) a step of forming a substrate product for aIII-nitride semiconductor laser device, based on the estimation; (e) astep of forming a scribed groove in the substrate product, using acondition of the forming; and (f) a step of performing breakup of thesubstrate product by press against the substrate product, afterformation of the scribed groove in the substrate product. Thesemiconductor device includes a substrate comprising a hexagonalIII-nitride semiconductor and a hexagonal III-nitride semiconductorregion formed on the substrate, or includes a substrate comprising ahexagonal III-nitride semiconductor.

According to this method, the scribed groove can be formed in thesubstrate product, based on the estimation. For this reason, a minimumdistance between an end of the scribed groove formed under the foregoingforming condition and a laser stripe of a semiconductor laser can bedetermined based on the estimation.

In the further aspect of the present invention, the substrate producthas a laser structure, an anode electrode, and a cathode electrode, thelaser structure including a substrate and a semiconductor region, thesubstrate comprising a hexagonal III-nitride semiconductor, thesemiconductor region being formed on a semipolar principal surface ofthe substrate. The c-axis of the hexagonal III-nitride semiconductor ofthe substrate tilts at an angle ALPHA with respect to the normal axistoward the m-axis of the hexagonal III-nitride semiconductor, and theangle ALPHA can be in a range of not less than 45° and not more than 80°or in a range of not less than 100° and not more than 135°.

A III-nitride semiconductor laser device according to an aspect of thepresent invention comprises: (a) a laser structure including a supportbase comprising a hexagonal III-nitride semiconductor and having asemipolar principal surface and a back surface, and a semiconductorregion provided on the semipolar principal surface of the support base;and (b) an electrode provided on the semiconductor region of the laserstructure. The semiconductor region includes a first conductivity typecladding layer, a second conductivity type cladding layer, and an activelayer provided between the first cladding layer and the second claddinglayer; the first conductivity type cladding layer, the secondconductivity type cladding layer, and the active layer are arrangedalong a normal axis to the semipolar principal surface; the c-axis ofthe hexagonal III-nitride semiconductor of the support base tilts at anangle ALPHA with respect to the normal axis toward the axis of thehexagonal III-nitride semiconductor; the angle ALPHA is in a range ofnot less than 45° and not more than 80° or in a range of not less than100° and not more than 135°; the laser structure includes first andsecond surfaces; the first surface is a surface opposite to the secondsurface; the semiconductor region is located between the first surfaceand the support base; the laser structure has first and second scribedmarks at one end and the other end, respectively, of an edge of thefirst surface at an end of the laser structure; the first and secondscribed marks extend from the first surface; the end of the laserstructure has a fractured face connecting edges of the first and secondscribed marks and the edges of the first and second surfaces of thelaser structure; a laser cavity of the III-nitride semiconductor laserdevice includes the fractured face; the first and second scribed marksextend along a predetermined plane defined by the a-axis of thehexagonal III-nitride semiconductor and the normal axis.

In this III-nitride semiconductor laser device, the first and secondscribed marks are provided along the predetermined plane (referred to as“a-n plane”). These scribed marks are formed from scribed grooves. Thescribed grooves guide progress of fracture. For this reason, thefracture proceeds in the direction of the a-n plane to form thefractured face. In this III-nitride semiconductor laser device, thefractured face for the laser cavity intersects with an m-n plane definedby the m-axis of the hexagonal III-nitride semiconductor and the normalaxis, and therefore a laser waveguide can be provided so as to extend ina direction of an interesting line between the m-n plane and thesemipolar plane. For this reason, it is feasible to provide theIII-nitride semiconductor laser device with the laser cavity enabling alow threshold current.

Furthermore, in this III-nitride semiconductor laser device, when theangle is in a range of less than 45° or in a range of more than 135°, anend face formed by press is highly likely to be comprised of an m-plane.When the angle is in a range of more than 80° and less than 100°, thedesired flatness and perpendicularity might not be achieved. Therefore,this III-nitride semiconductor laser device can be provided as theIII-nitride semiconductor laser device with the laser cavity enablingthe low threshold current, on the semipolar plane of the support basetilting from the c-axis toward the m-axis of the hexagonal III-nitride.

The above objects and the other objects, features, and advantages of thepresent invention can more readily become apparent in view of thefollowing detailed description of the preferred embodiments of thepresent invention proceeding with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing schematically showing a structure of a III-nitridesemiconductor laser device according to an embodiment of the presentinvention.

FIG. 2 is a drawing showing a band structure in an active layer in theIII-nitride semiconductor laser device.

FIG. 3 is a drawing showing polarization of emission in the active layerof the III-nitride semiconductor laser device.

FIG. 4 is a drawing showing a relation between an end face of theIII-nitride semiconductor laser device and an m-plane of the activelayer.

FIG. 5 is a step flowchart showing major steps in a method forfabricating a III-nitride semiconductor laser device according to anembodiment of the present invention.

FIG. 6 is a drawing schematically showing major steps in the method forfabricating the III-nitride semiconductor laser device according to theembodiment.

FIG. 7 is a drawing showing a scanning electron microscope image of acavity end face, along with a {20-21} plane in crystal lattices.

FIG. 8 is a drawing showing a structure of a laser diode shown inExample 1.

FIG. 9 is a drawing showing a relation of determined polarization degreeρ versus threshold current density.

FIG. 10 is a drawing showing a relation of tilt angle of the c-axistoward the m-axis of GaN substrate versus lasing yield.

FIG. 11 is a drawing showing a relation of stacking fault density versuslasing yield.

FIG. 12 is a drawing showing a relation of substrate thickness versuslasing yield.

FIG. 13 is a drawing showing an example of a cathodoluminescence (CL)image of a region around a scribed groove.

FIG. 14 is a drawing showing an example of a secondary electron emission(SE) image of a region around a scribed groove.

FIG. 15 is a drawing showing (a) an SE image and (b) a CL image of across section of a scribed groove.

FIG. 16 is a drawing showing major steps in a method for evaluatingdamage.

FIG. 17 is a drawing showing a list of dimensions used in an experimentin formation of scribed grooves for obtaining chip widths of 200 μm, 150μm, and 100 μm.

FIG. 18 is a drawing showing an arrangement of scribed grooves SG andlaser stripes LS.

FIG. 19 is a drawing schematically showing an example of a semiconductorlaser having the gain guiding structure.

FIG. 20 is a drawing schematically showing an example of an index guidedlaser having the ridge structure.

FIG. 21 is a drawing showing dependence of lasing yield on distancesbetween a waveguide and scribed grooves.

FIG. 22 is a drawing showing angles between (20-21) plane and otherplane orientations (indices).

FIG. 23 is a drawing showing atomic arrangements in (20-21) plane,(−101-6) plane, and (−1016) plane.

FIG. 24 is a drawing showing atomic arrangements in (20-21) plane,(−101-7) plane, and (−1017) plane.

FIG. 25 is a drawing showing atomic arrangements in (20-21) plane,(−101-8) plane, and (−1018) plane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The expertise of the present invention can be readily understood in viewof the following detailed description with reference to the accompanyingdrawings provided by way of illustration only. The following willdescribe embodiments of the III-nitride semiconductor laser device andthe method for fabricating the III-nitride semiconductor laser deviceaccording to the present invention, with reference to the accompanyingdrawings. The same portions will be denoted by the same referencesymbols as much as possible.

FIG. 1 is a drawing schematically showing a structure of a III-nitridesemiconductor laser device according to an embodiment of the presentinvention. The III-nitride semiconductor laser device 11 has again-guiding type structure, but embodiments of the present inventionare not limited to the gain-guiding type structure. The III-nitridesemiconductor laser device 11 has a laser structure 13 and an electrode15. The laser structure 13 includes a support base 17 and asemiconductor region 19. The support base 17 comprises a hexagonalIII-nitride semiconductor and has a semipolar principal surface 17 a anda back surface 17 b. The semiconductor region 19 is provided on thesemipolar principal surface 17 a of the support base 17. The electrode15 is provided on the semiconductor region 19 of the laser structure 13.The semiconductor region 19 includes a first cladding layer 21, a secondcladding layer 23, and an active layer 25. The first cladding layer 21comprises a first conductivity type GaN-based semiconductor, e.g.,n-type AlGaN, n-type InAlGaN, or the like. The second cladding layer 23comprises a second conductivity type GaN-based semiconductor, e.g.,p-type AlGaN, p-type InAlGaN, or the like. The active layer 25 isprovided between the first cladding layer 21 and the second claddinglayer 23. The active layer 25 includes GaN-based semiconductor layers,and the GaN-based semiconductor layers are, for example, well layers 25a. The active layer 25 includes bather layers 25 b comprising aGaN-based semiconductor, and the well layers 25 a and the barrier layers25 b are alternately arranged. The well layers 25 a comprise, forexample, InGaN or the like, and the barrier layers 25 b, for example,GaN, InGaN, or the like. The active layer 25 can include a quantum wellstructure provided so as to generate light at the wavelength of not lessthan 430 nm and not more than 600 nm. Use of a semipolar plane issuitable for generation of light at the wavelength of not less than 500nm (green) and not more than 600 nm. The transverse spread of light inthe optical waveguide is related to the wavelength of guided light. Thedistances W1, W2 according to the present embodiment are suitablyapplicable in the aforementioned wavelength range. The first claddinglayer 21, the second cladding layer 23, and the active layer 25 arearranged along a normal axis NX to the semipolar principal surface 17 a.In the III-nitride semiconductor laser device 11, the laser structure 13includes a first fractured face 27 and a second fractured face 29intersecting with an m-n plane defined by the m-axis of the hexagonalIII-nitride semiconductor and the normal axis NX.

Referring to FIG. 1, there are an orthogonal coordinate system S and acrystal coordinate system CR depicted. The normal axis NX is directedalong a direction of the Z-axis of the orthogonal coordinate system S.The semipolar principal surface 17 a extends in parallel with apredetermined plane defined by the X-axis and the Y-axis of theorthogonal coordinate system S. In FIG. 1, a typical c-plane Sc is alsodepicted. The c-axis of the hexagonal III-nitride semiconductor of thesupport base 17 tilts at a finite angle ALPHA with respect to the normalaxis NX toward the m-axis of the hexagonal III-nitride semiconductor.

The III-nitride semiconductor laser device 11 further has an insulatingfilm 31. The insulating film 31 covers a surface 19 a of thesemiconductor region 19 of the laser structure 13, and the semiconductorregion 19 is located between the insulating film 31 and the support base17. The support base 17 comprises a hexagonal III-nitride semiconductor.The insulating film 31 has an aperture 31 a, and the aperture 31 aextends in a direction of an intersecting line LIX between the surface19 a of the semiconductor region 19 and the foregoing m-n plane and is,for example, a stripe shape. The electrode 15 is in contact with thesurface 19 a of the semiconductor region 19 (e.g., a contact layer 33 ofthe second conductivity type) through the aperture 31 a and extends inthe direction of the foregoing intersecting line LIX. In the III-nitridesemiconductor laser device 11, a laser waveguide includes the firstcladding layer 21, the second cladding layer 23, and the active layer25, and extends in the direction of the foregoing intersecting line LIX.For example, in the case of a gain guiding type laser, the aperture 31 aof the insulating film 31 has, for example, the stripe shape, and thedirection of the laser waveguide is the extending direction of thestripe aperture. In the case of a ridge type laser, the semiconductorregion 19 of the laser structure 13 has the ridge structure, and thedirection of the laser waveguide is the extending direction of the ridgestructure. A waveguide vector LGV shows the direction of the laserwaveguide.

In the III-nitride semiconductor laser device 11, the first fracturedface 27 and the second fractured face 29 intersect with the m-n planedefined by the m-axis of the hexagonal III-nitride semiconductor and thenormal axis NX. A laser cavity of the III-nitride semiconductor laserdevice 11 includes the first and second fractured faces 27, 29, and thelaser waveguide extends from one to the other of the first fracturedface 27 and the second fractured face 29. The laser structure 13includes a first surface 13 a and a second surface 13 b, and the firstsurface 13 a is a surface opposite to the second surface 13 b. The firstand second fractured faces 27, 29 each extend from an edge 13 c of thefirst surface 13 a to an edge 13 d of the second surface 13 b. The firstand second fractured faces 27, 29 are different from the conventionalcleaved facets such as c-planes, m-planes, or a-planes. Thesemiconductor region 17 is located between the first surface 13 a andthe support base 17 (or substrate). The laser structure 13 includes alaser stripe extending in a direction of a waveguide axis above thesemipolar principal surface 17 a of the support base 17. The waveguideaxis extends from one to the other of the first and second fracturedfaces 27, 29. The waveguide axis is directed in the direction of thewaveguide vector LGV extending in the direction from the first fracturedface 27 to the second fractured face 29.

In this III-nitride semiconductor laser device 11, the first and secondfractured faces 27, 29 forming the laser cavity intersect with the m-nplane. This allows for provision of the laser waveguide extending in thedirection of the intersecting line between the m-n plane and thesemipolar plane 17 a. For this reason, the III-nitride semiconductorlaser device 11 has the laser cavity enabling a low threshold current.

The laser structure 13 has first and second recesses 28, 30 providedeach at a portion of edge 13 c of the first surface 13 a in a fracturedface (reference is made to the “first fractured face 27” in thedescription hereinafter). The first and second recesses 28, 30 includefirst and second scribed marks, respectively, left in each semiconductordevice separated by fracture guided by scribed grooves. The first andsecond recesses 28, 30 extend from the first surface 13 a of the laserstructure 13. Bottom ends 28 a, 30 a of the first and second recesses28, are located apart from edge 13 d of the second surface 13 b of thelaser structure. The first recess 28 has an end 28 b at the firstsurface 13 a, and the second recess 30 has an end 30 b at the firstsurface 13 a. A first distance W1 between the end 28 b of the firstrecess 28 and the laser stripe is smaller than a second distance W2between the end 30 b of the second recess 30 and the laser stripe.

The laser structure 13 includes one end 14 a, the other end 14 b, and anintermediate portion 14 c, and the intermediate portion 14 c is locatedbetween the one end 14 a and the other end 14 b. In one example of thelaser structure 13, the first and second scribed marks are provided atone end and the other end, respectively, of the edge of the firstsurface 13 a at the end 14 a. The first and second scribed marks extendalong an a-n plane defined by the a-axis of the hexagonal III-nitridesemiconductor and the normal axis NX. In the present embodiment, thefirst and second scribed marks extend from the first surface 13 a orepitaxially grown surface toward the back surface 17 b of the supportbase 17. At the end 14 a of the laser structure 13, the fractured face27 is formed so as to connect edges 28 e, 30 e of the first and secondscribed marks and the edges 13 c, 13 d of the first and second surfaces13 a, 13 b of the laser structure 13. For this reason, the laser cavityof the III-nitride semiconductor laser device 11 includes the fracturedface 27, and in the laser structure 13, the laser stripe extending inthe direction of the waveguide vector LGV above the semipolar principalsurface 17 a of the support base 17 is provided between the first andsecond scribed marks at the end 14 a. The distance between the end ofthe first scribed mark and the laser stripe corresponds to the distancerepresented by reference sign W1 defined for the end 28 b of the firstrecess 28 in the present embodiment. Furthermore, the distance betweenthe end of the second scribed mark and the laser stripe corresponds tothe distance represented by reference sign W2 defined for the end 30 bof the second recess 30 in the present embodiment. Each of the first andsecond scribed marks is formed from a scribed groove by fracture, andthe scribed groove guides progress of the fracture. Furthermore, thefirst distance between the laser stripe and the end of the first scribedmark can be made smaller than the second distance between the laserstripe and the end of the second scribed mark, which can reduce thedevice width WD of the laser device.

In the III-nitride semiconductor laser device 11, the first distance W1can be not less than 20 μm. In this III-nitride semiconductor laserdevice, the end 28 b of the recess 28 can be located up to the neardistance of 20 μm from the laser stripe. The first distance W1 can beless than 50 μm. In this III-nitride semiconductor laser device 11, thefirst distance W1 is preferably less than 50 μm, for reduction in devicewidth. Furthermore, the first distance W1 may be less than 70 μm.

In the III-nitride semiconductor laser device 11, the first distance W1can be less than 50 μm, and the second distance W2 not less than 50 μm.In this III-nitride semiconductor laser device 11, the first distance W1can be made smaller than the second distance W2, which can reduce thedevice width WD of the laser device.

The width WD of the III-nitride semiconductor laser device 11 can be notmore than 200 μm. The III-nitride semiconductor laser device 11 can beprovided in the device width of not more than 200 μm.

In the III-nitride semiconductor laser device 11, the first recess 28includes a slope portion 28 c where a bottom 28 a of the recess 28 tiltstoward the end 28 b, and in the slope portion 28 c, the depth of thescribed groove becomes shallower, for example, in the positive directionof the Y-axis. The first recess 28 may include a substantially flatportion 28 d with a tilt smaller than that of the slope portion 28 c,and the flat portion 28 d is adjacent to the slope portion 28 c. Thesecond recess 30 includes a slope portion 30 c where a bottom 30 a ofthe recess 30 tilts toward the end 30 b, and in the slope portion 30 c,the depth of the scribed groove becomes deeper, for example, in thepositive direction of the Y-axis. The second recess 30 may include asubstantially flat portion 30 d with a tilt smaller than that of theslope portion 30 c, and the flat portion 30 d is adjacent to this slopeportion 30 c. The orientation of the tilt at the slope portion 28 c ofthe first recess 28 is opposite to that at the slope portion 30 c of thesecond recess 30. A first length LS1 of the slope portion 28 c of thefirst recess 28 is preferably longer than a second length LS2 of theslope portion 30 c of the second recess 30. In this III-nitridesemiconductor laser device 11, the scribed grooves are formed so thatthe first length LS1 is longer than the second length LS2, whereby it isfeasible to reduce an adverse effect on laser operation from damage nearthe end 28 b of the first recess 28 with damage greater than that nearthe end 30 b of the second recess 30. For example, a second length LP2of the flat portion 30 c of the second recess 30 can be not less than afirst length LP1 of the flat portion 28 d of the first recess 28.

The above description concerns the recesses 28, 30 in the fractured face27. The III-nitride semiconductor laser device 11 may include afractured face 29 at the end 14 b, and the fractured face 29 can includerecesses 32, 34. The recesses 32, 34 each can have the sameconfiguration and size as the recesses 28, 30, but do not have to belimited to this.

The electrode 15 is connected through the aperture 31 a of theinsulating film 31 to the semiconductor region 17 of the laser structure13. When the III-nitride semiconductor laser device 11 has the gainguiding structure, the first distance W1 can be defined as a distancebetween the aperture 31 a of the insulating film 31 and the end 28 b ofthe first recess 28, and the second distance W2 as a distance betweenthe aperture 31 a of the insulating film 31 and the end 30 b of thesecond recess 30. In this III-nitride semiconductor laser device 11,each of the first and second distances W1, W2 can be defined by thedistance between the aperture 31 a of the insulating film 31 and the end28 b or 30 b of the first and second recesses 28, 31. The aperture 31 acan have, for example, a stripe shape.

As another example, where the semiconductor region 13 of the laserstructure 13 has the ridge structure, the first distance W1 can bedefined as a distance between the ridge structure and the end 28 b ofthe first recess 28, and the second distance W2 as a distance betweenthe ridge structure and the end 30 b of the second recess 30.

The III-nitride semiconductor laser device 11 includes an n-side lightguide layer 35 and a p-side light guide layer 37. The n-side light guidelayer 35 includes a first portion 35 a and a second portion 35 b, andthe n-side light guide layer 35 comprises, for example, GaN, InGaN, orthe like. The p-side light guide layer 37 includes a first portion 37 aand a second portion 37 b, and the p-side light guide layer 37comprises, for example, GaN, InGaN, or the like. A carrier block layer39 is provided, for example, between the first portion 37 a and thesecond portion 37 b. Another electrode 41 is provided on the backsurface 17 b of the support base 17, and the electrode 41 covers, forexample, the back surface 17 b of the support base 17.

FIG. 2 is a drawing showing a band structure in the active layer in theIII-nitride semiconductor laser device. FIG. 3 is a drawing showingpolarization of emission in the active layer 25 of the III-nitridesemiconductor laser device 11. FIG. 4 is a drawing schematically showinga cross section defined by the c-axis and the m-axis. With reference topart (a) of FIG. 2, there are three possible transitions between theconduction band and valence bands in the vicinity of Γ point of the bandstructure BAND. There is a relatively small energy difference betweenband A and band B. An emission by transition Ea between the conductionband and band A is polarized in the a-axis direction, and an emission bytransition Eb between the conduction band and band B is polarized in theprojected direction of the c-axis on the principal surface. Concerninglaser oscillation, a threshold of transition Ea is smaller than athreshold of transition Eb.

With reference to part (b) of FIG. 2, there are shown spectra of lightin the LED mode in the III-nitride semiconductor laser device 11. Thelight in the LED mode includes a polarization component I1 in thedirection of the a-axis of the hexagonal III-nitride semiconductor, anda polarization component I2 in the projected direction of the c-axis ofthe hexagonal III-nitride semiconductor on the principal surface, andthe polarization component I1 is larger than the polarization componentI2. Degree of polarization ρ is defined by (I1−I2)/(I1+I2). Using thelaser cavity of the III-nitride semiconductor laser device 11, thedevice can be lased to emit light in a mode with large emissionintensity in the LED mode.

As shown in FIG. 3, the device may be further provided with dielectricmultilayer film 43 a, 43 b on at least one of the first and secondfractured faces 27, 29 or with both on the respective faces. An end facecoat is also applicable to the fractured faces 27, 29. The end face coatallows adjustment of reflectance.

As shown in part (b) of FIG. 3, the laser light L from the active layer25 is polarized in the direction of the a-axis of the hexagonalIII-nitride semiconductor. In this III-nitride semiconductor laserdevice 11, a band transition allowing for implementation of a lowthreshold current has polarized nature. The first and second fracturedfaces 27, 29 for the laser cavity are different from the conventionalcleaved facets such as c-planes, m-planes, or a-planes. However, thefirst and second fractured faces 27, 29 have flatness andperpendicularity enough as mirrors for the cavity. For this reason, byusing the first and second fractured faces 27, 29 and the laserwaveguide extending between these fractured faces 27, 29, as shown inpart (b) of FIG. 3, it becomes feasible to achieve low-threshold laseroscillation through the use of the emission by transition Ea strongerthan the emission by transition Eb polarized in the projected directionof the c-axis on the principal surface.

In the III-nitride semiconductor laser device 11, an end face 17 c ofthe support base 17 and an end face 19 c of the semiconductor region 19are exposed in each of the first and second fractured faces 27, 29, andthe end face 17 c and the end face 19 c are covered by the dielectricmultilayer film 43 a. An angle BETA between a normal vector NA to theend face 17 c of the support base 17 and an end face 25 c in the activelayer 25, and an m-axis vector MA of the active layer 25 is defined bycomponent (BETA)₁ defined on a first plane S1 defined by the c-axis andm-axis of the III-nitride semiconductor, and component (BETA)₂ definedon a second plane S2 (which is not shown for easier understanding but isreferred to as “S2”) perpendicular to the first plane S1 (which is notshown for easier understanding but is referred to as “S1”) and thenormal axis NX. The component (BETA)₁ is preferably in a range of notless than (ALPHA−5)° and not more than (ALPHA+5)° on the first plane S1defined by the c-axis and m-axis of the III-nitride semiconductor. Thisangle range is shown as an angle between a typical m-plane S_(M) and areference plane F_(A) in FIG. 4. The typical m-plane S_(M) is depictedfrom the inside to the outside of the laser structure in FIG. 4, foreasier understanding. The reference plane F_(A) extends along the endface 25 c of the active layer 25. This III-nitride semiconductor laserdevice 11 has the end faces satisfying the aforementionedperpendicularity, as to the angle BETA taken from one to the other ofthe c-axis and the m-axis. The component (BETA)₂ is preferably in arange of not less than −5° and not more than +5° on the second plane S2.Here, BETA²=(BETA)₁ ²+(BETA)₂ ². In this case, the end faces 27, 29 ofthe III-nitride semiconductor laser device 11 satisfy the aforementionedperpendicularity as to the angle defined on the plane perpendicular tothe normal axis NX to the semipolar plane 17 a.

Referring again to FIG. 1, in the III-nitride semiconductor laser device11 the thickness DSUB of the support base 17 is preferably not more than400 μm. This III-nitride semiconductor laser device is suitable forobtaining good-quality fractured faces for the laser cavity. In theIII-nitride semiconductor laser device 11, the thickness DSUB of thesupport base 17 is more preferably not less than 50 μm and not more than100 μm. This III-nitride semiconductor laser device 11 is more suitablefor obtaining good-quality fractured faces for the laser cavity.Furthermore, handling becomes easier and the production yield becomeshigher.

In the III-nitride semiconductor laser device 11, the angle ALPHAbetween the normal axis NX and the c-axis of the hexagonal III-nitridesemiconductor is preferably not less than 45° and preferably not morethan 80°. Furthermore, the angle ALPHA is preferably not less than 100°and preferably not more than 135°. When the angle is in a range of lessthan 45° or in a range of more than 135°, the end faces made by pressare highly likely to be comprised of m-planes. When the angle is in arange of more than 80° and less than 100°, it could result in failing toachieve the desired flatness and perpendicularity.

In the III-nitride semiconductor laser device 11, more preferably, theangle ALPHA between the normal axis NX and the c-axis of the hexagonalIII-nitride semiconductor is not less than 63° and not more than 80°.Furthermore, the angle ALPHA is more preferably not less than 100° andnot more than 117°. When the angle is in a range of less than 63° or ina range of more than 117°, an m-plane can appear in part of an end facemade by press. When the angle is in a range of more than 80° and lessthan 100°, it could result in failing to achieve the desired flatnessand perpendicularity.

The semipolar principal surface 17 a can be any one of a {20-21} plane,a {10-11} plane, a {20-2-1} plane, and a {10-1-1} plane. Furthermore, asurface with a slight slant in a range of not less than −4° and not morethan +4° from these planes is also suitable for the principal surface.On the semipolar surface 17 a of one of these typical planes, it isfeasible to provide the first and second end faces 27, 29 with flatnessand perpendicularity enough to construct the laser cavity of theIII-nitride semiconductor laser device 11. Furthermore, the end faceswith sufficient flatness and perpendicularity are obtained in an angularrange across these typical plane orientations.

In the III-nitride semiconductor laser device 11, the stacking faultdensity of the support base 17 can be not more than 1×10⁴ cm⁻¹. Sincethe stacking fault density is not more than 1×10⁴ cm⁻¹, the flatnessand/or perpendicularity of the fractured faces are/is less likely to bedisturbed for a certain accidental reason. The support base 17 cancomprise any one of GaN, AlN, AlGaN, InGaN, and InAlGaN. When thesubstrate comprising any one of these GaN-based semiconductors is used,the end faces 27, 29 applicable to the cavity can be obtained. When anAlN or AlGaN substrate is used, it is feasible to increase the degree ofpolarization and to enhance optical confinement by virtue of lowrefractive index. When an InGaN substrate is used, it is feasible todecrease the lattice mismatch rate between the substrate and the lightemitting layer and to improve crystal quality.

FIG. 5 is a drawing showing major steps in a method for fabricating aIII-nitride semiconductor laser device according to an embodiment of thepresent invention. With reference to part (a) of FIG. 6, a substrate 51is shown. Step S101 is to prepare the substrate 51 for fabrication ofthe III-nitride semiconductor laser device. The c-axis (vector VC) ofthe hexagonal III-nitride semiconductor of the substrate 51 tilts at thefinite angle ALPHA with respect to the normal axis NX toward the m-axis(vector VM) of the hexagonal III-nitride semiconductor. For this reason,the substrate 51 has a semipolar principal surface 51 a comprising thehexagonal III-nitride semiconductor.

Step S102 is to form a substrate product SP. In part (a) of FIG. 6, thesubstrate product SP is depicted as a member of a nearly disklike shape,but the shape of the substrate product SP is not limited to this. Forobtaining the substrate product SP, step S103 is first carried out toform a laser structure 55. The laser structure 55 includes asemiconductor region 53 and the substrate 51, and step S103 is to formthe semiconductor region 53 on the semipolar principal surface 51 a. Afirst conductivity type GaN-based semiconductor region 57, a lightemitting layer 59, and a second conductivity type GaN-basedsemiconductor region 61 are grown in order on the semipolar principalsurface 51 a, for forming the semiconductor region 53. The GaN-basedsemiconductor region 57 can include, for example, an n-type claddinglayer, and the GaN-based semiconductor region 61 can include, forexample, a p-type cladding layer. The light emitting layer 59 isprovided between the GaN-based semiconductor region 57 and the GaN-basedsemiconductor region 61 and can include an active layer, light guidelayers, an electron block layer, and so on. The GaN-based semiconductorregion 57, the light emitting layer 59, and the second conductivity typeGaN-based semiconductor region 61 are arranged along the normal axis NXto the semipolar principal surface 51 a. These semiconductor layers areepitaxially grown. The surface of the semiconductor region 53 is coveredby an insulating film 54. The insulating film 54 comprises, for example,silicon oxide. The insulating film 54 has an aperture 54 a. The aperture54 a is, for example, a stripe shape.

Step S104 is to form an anode electrode 58 a and a cathode electrode 58b on the laser structure 55. Before forming the electrode on the backsurface of the substrate 51, the back surface of the substrate used incrystal growth is polished to form a substrate product SP in a desiredthickness DSUB. In formation of the electrodes, for example, the anodeelectrode 58 a is formed on the semiconductor region 53, and the cathodeelectrode 58 b is formed on the back surface (polished surface) 51 b ofthe substrate 51. The anode electrode 58 a extends in the X-axisdirection, and the cathode electrode 58 b covers the entire area of theback surface 51 b. These steps result in forming the substrate productSP. The substrate product SP includes a first surface 63 a, and a secondsurface 63 b located opposite thereto. The semiconductor region 53 islocated between the first surface 63 a and the substrate 51.

Step S105 is, as shown in part (b) of FIG. 6, to scribe the firstsurface 63 a of the substrate product SP. This scribing step is carriedout with a laser scriber 10 a. This scribing step results in formingscribed grooves 65 a, e.g., in the positive direction of the Y-axis. Inpart (b) of FIG. 6, five scribed grooves are already formed, andformation of a scribed groove 65 b is in progress with a laser beam LB.The length of the scribed grooves 65 a is shorter than the length of anintersecting line MS between an a-n plane defined by the a-axis of thehexagonal III-nitride semiconductor and the normal axis NX, and thefirst surface 63 a, and the laser beam LB is applied to a part of theintersecting line MS. By the application with the laser beam LB, groovesextending in the specific direction and reaching the semiconductorregion are formed in the first surface 63 a. The scribed grooves 65 acan be formed, for example, at an edge of the substrate product SP. Inan example, the array of scribed grooves are formed by a scan with thelaser beam LB along the intersecting line MS.

Specifically, the first surface 63 a of the substrate product SP isscribed along a fracture line extending in the direction of the a-axisof the hexagonal III-nitride semiconductor (e.g., the positive directionof the Y-axis) to form first and second scribed grooves 64 a, 64 b.During the scribing, the laser beam scans in the positive direction ofthe Y-axis. Therefore, the first scribed groove 64 a is first formed andthen the second scribed groove 64 b is formed. With reference to part(b) of FIG. 6, there is shown a laser stripe extending in the directionof the waveguide axis (X-axis direction). The first scribed groove 64 a,the laser stripe LS, and the second scribed groove 64 b are arranged inorder in the direction of the a-axis of the hexagonal III-nitridesemiconductor. In the present embodiment, the laser stripe LS can bedefined, for example, by the aperture 54 a of the insulating film 54.The first scribed groove 64 a has an end 66 a at the first surface 63 a,and the second scribed groove 64 b has an end 66 b at the first surface63 a. The first distance W1 between the laser stripe LS and the end 66 aof the first scribed groove 64 a is smaller than the second distance W2between the laser stripe LS and the end 66 b of the second scribedgroove 64 b. The first and second scribed grooves 64 a, 64 b areadjacent to each other, and a distance between the end 66 a of the firstscribed groove 64 a and the end 66 b of the second scribed groove 64 bis smaller than the width of the III-nitride semiconductor laser device.The end 66 a of the first scribed groove 64 a is, for example, aterminal end in formation of a scribed groove, and the end 66 b of thesecond scribed groove 64 b is, for example, an initial end in formationof a scribed groove. In order to obtain the fractured face in which theextending direction of the scribed grooves (or scribed marks) isdescribed by the depth direction, the scribed groove space (or scribedmark space) is preferably not less than 40 μm and not more than 800 μm.

The first distance W1 can be not less than 20 μm. On the substrateproduct SP, the size of a damaged region near one end 66 a of thescribed groove 64 a is smaller than the size of a damaged region nearthe other end 66 b of the scribed groove 64 b. The end of the scribedgroove with the smaller size of the damaged region can be located up tothe minimum distance of about 20 μm from the laser stripe LS.Furthermore, the end of the scribed groove with the larger size of thedamaged region can be located up to the minimum distance of about 50 μmfrom the laser stripe. The first distance W1 can be, for example, lessthan 50 μm.

The first distance W1 can be less than 50 μm and the second distance W2not less than 50 μm. Since the adjacent scribed grooves are formed sothat the first distance W1 is smaller than the second distance W2, thedevice width of the laser device can be reduced. This method allows thelaser device to be formed in the device width of not more than 200 μm.

Step S106 is, as shown in part (c) of FIG. 6, to implement breakup ofthe substrate product SP by press against the second surface 63 b of thesubstrate product SP to form a substrate product SP1 and a laser barLB1. The press is carried out with a breaking device, for example, likea blade 69. The blade 69 includes an edge 69 a extending in onedirection, and at least two blade faces 69 b, 69 c defining the edge 69a. The press on the substrate product SP1 is carried out on a supportdevice 70. The support device 70 includes a support table 70 a and arecess 70 b, and the recess 70 b extends in one direction. The recess 70b is formed in the support table 70 a. The orientation and position ofthe scribed groove 65 a of the substrate product SP1 are aligned withthe extending direction of the recess 70 b of the support device 70 toposition the substrate product SP1 to the recess 70 b on the supportdevice 70. The orientation of the edge of the breaking device is alignedwith the extending direction of the recess 70 b, and the edge of thebreaking device is pressed against the substrate product SP1 from adirection intersecting with the second surface 63 b. The intersectingdirection is preferably an approximately normal direction to the secondsurface 63 b. This implements the breakup of the substrate product SP toform the substrate product SP1 and laser bar LB1. The press results informing the laser bar LB1 with first and second end faces 67 a, 67 b,and these end faces 67 a, 67 b have perpendicularity and flatness enoughto make at least a part of the light emitting layer applicable to thecavity mirrors of the semiconductor laser.

The laser bar LB1 thus formed has the first and second end faces 67 a,67 b formed by the aforementioned breakup, and each of the end faces 67a, 67 b extends from the first surface 63 a to the second surface 63 b.For this reason, the end faces 67 a, 67 b form the laser cavity of theIII-nitride semiconductor laser device and intersect with the XZ plane.This XZ plane corresponds to the m-n plane defined by the m-axis of thehexagonal III-nitride semiconductor and the normal axis NX.

According to this method, the first surface 63 a of the substrateproduct SP is scribed in the direction of the a-axis of the hexagonalIII-nitride semiconductor and thereafter the breakup of the substrateproduct SP is carried out by press against the second surface 63 b ofthe substrate product SP, thereby forming the new substrate product SP1and the laser bar LB1. For this reason, the first and second end faces67 a, 67 b are formed in the laser bar LB1 so as to intersect with them-n plane. This end face forming method provides the first and secondend faces 67 a, 67 b with flatness and perpendicularity enough toconstruct the laser cavity of the III-nitride semiconductor laserdevice.

In this method, the laser waveguide formed extends in the direction oftilt of the c-axis of the hexagonal III-nitride. The cavity mirror endfaces allowing for provision of this laser waveguide are formed withoutuse of dry-etched facets. In this method, when the angle is in a rangeof less than 45° or in a range of more than 135°, end faces made bypress are highly likely to be comprised of m-planes. When the angle isin a range of more than 80° and less than 100°, it might result infailing to achieve the desired flatness and perpendicularity.

This method involves the fracture of the substrate product SP1, therebyforming the new substrate product SP1 and the laser bar LB1. Step S107is to repeatedly carry out the breakup by press to produce many laserbars. This fracture is brought about using the scribed groove 65 ashorter than a fracture line BREAK of the laser bar LB1.

In this method, the scribed grooves 64 a, 64 b and laser stripes LS arealternately arranged in the a-axis direction on the substrate productSP1. A scribed groove is formed between two adjacent laser stripes.Damage caused by formation of the scribed grooves is not isotropic inthe vicinity of the scribed grooves 64 a, 64 b. Namely, damaged regionsdue to formation of the scribed grooves 64 a, 64 b are formed inasymmetry around the scribed grooves. For this reason, the size of thedamaged region near one end 66 a of the scribed groove 64 a is smallerthan the size of the damaged region near the other end 66 b of thescribed groove 64 b. When attention is focused on one laser stripe amongthe array of laser stripes LS, the first distance (distance between thelaser stripe LS and the end 66 a of the first scribed groove 64 a asshown in part (b) of FIG. 6) W1 can be made smaller than the seconddistance (distance between the laser stripe LS and the end 66 b of thesecond scribed groove 64 b) W2. Therefore, the device width of the laserdevice can be reduced.

Step S108 is to form dielectric multilayer films on the end faces 67 a,67 b of the laser bar LB1 to form a laser bar product. Step S109 is tobreak this laser bar product into chips of individual semiconductorlasers.

In the fabrication method according to the present embodiment, the angleALPHA can be in a range of not less than 45° and not more than 80° or ina range of not less than 100° and not more than 135°. When the angle isin a range of less than 45° or in a range of more than 135°, the endface made by press becomes highly likely to be comprised of an m-plane.When the angle is in a range of more than 80° and less than 100°, itcould result in failing to achieve desired flatness andperpendicularity. More preferably, the angle ALPHA can be in a range ofnot less than 63° and not more than 80° or in a range of not less than100° and not more than 117°. When the angle is in a range of less than45° or in a range of more than 135°, an m-plane can appear in part of anend face formed by press. When the angle is in a range of more than 80°and less than 100°, it could result in failing to achieve the desiredflatness and perpendicularity. The semipolar principal surface 51 a canbe any one of a {20-21} plane, a {10-11} plane, a {20-2-1} plane, and a{10-1-1} plane. Furthermore, a surface with a slight slant in a range ofnot less than −4° and not more than +4° from these planes is alsosuitable for the principal surface. On these typical semipolar planes,it is feasible to provide the end faces for the laser cavity withflatness and perpendicularity enough to construct the laser cavity ofthe III-nitride semiconductor laser device.

The substrate 51 can comprise any one of GaN, AlN, AlGaN, InGaN, andInAlGaN. When the substrate used comprises any one of these GaN-basedsemiconductors, it is feasible to obtain the end faces applicable to thelaser cavity. The substrate 51 preferably comprises GaN.

In the step S104 of forming the substrate product SP, the semiconductorsubstrate used in crystal growth can be one subjected to processing suchas slicing or grinding so that the substrate thickness becomes not morethan 400 μm, and having the second surface 63 b of a processed surfaceformed by polishing. In this substrate thickness, the end faces 67 a, 67b can be formed in good yield, with flatness and perpendicularity enoughto construct the laser cavity of the III-nitride semiconductor laserdevice or without ion damage. More preferably, the second surface 63 bis a polished surface formed by polishing, and the substrate thicknessafter polishing is not more than 100 μm. For relatively easily handlingthe substrate product SP, the substrate thickness is preferably not lessthan 50 μm.

In the production method of the laser end faces according to the presentembodiment, the angle BETA explained with reference to FIG. 3 is alsodefined in the laser bar LB1. In the laser bar LB1, the component(BETA)₁ of the angle BETA is preferably in a range of not less than(ALPHA−5)° and not more than (ALPHA+5)° on a first plane (planecorresponding to the first plane S1 in the description with reference toFIG. 3) defined by the c-axis and m-axis of the III-nitridesemiconductor. The end faces 67 a, 67 b of the laser bar LB1 satisfy theaforementioned perpendicularity as to the angle component of the angleBETA taken from one to the other of the c-axis and the m-axis. Thecomponent (BETA)₂ of the angle BETA is preferably in a range of not lessthan −5° and not more than +5° on a second plane (plane corresponding tothe second plane S2 shown in FIG. 3). In this case, the end faces 67 a,67 b of the laser bar LB1 satisfy the aforementioned perpendicularity asto the angle component of the angle BETA defined on the planeperpendicular to the normal axis NX to the semipolar plane 51 a.

The end faces 67 a, 67 b are formed by break by press against theplurality of GaN-based semiconductor layers epitaxially grown on thesemipolar plane 51 a. Since they are epitaxial films on the semipolarplane 51 a, the end faces 67 a, 67 b are not cleaved facets with a lowplane index like c-planes, m-planes, or a-planes which have been usedheretofore for the conventional cavity mirrors. However, through thebreak of the stack of epitaxial films on the semipolar plane 51 a, theend faces 67 a, 67 b have the flatness and perpendicularity applicableas cavity mirrors.

Example 1

A semipolar-plane GaN substrate is prepared, and perpendicularity of afractured face is observed as described below. The substrate used is a{20-21}-plane GaN substrate cut at the angle of 75° toward the m-axisout of a (0001) GaN ingot thickly grown by HVPE. The principal surfaceof the GaN substrate is mirror-finished, and the back surface is in aground pear-skin state. The thickness of the substrate is 370 μm.

On the back side in the pear-skin state, a marking line is drawnperpendicularly to the projected direction of the c-axis on theprincipal surface of the substrate, with a diamond pen, and thereafterthe substrate is fractured by press. For observing the perpendicularityof the resultant fractured face, the substrate is observed from thea-plane direction with a scanning electron microscope.

Part (a) of FIG. 7 is a scanning electron microscope image of thefractured face observed from the a-plane direction, and the right endface is the fractured face. It is seen that the fractured face hasflatness and perpendicularity to the semipolar principal surface.

Example 2

It is found in Example 1 that in the GaN substrate having the semipolar{20-21} plane, the fractured face obtained by drawing the marking lineperpendicular to the projected direction of the c-axis on the principalsurface of the substrate and pressing the substrate has the flatness andperpendicularity to the principal surface of the substrate. For checkingapplicability of this fractured face to the laser cavity, a laser diodeshown in FIG. 8 is grown by metal-organic vapor phase epitaxy asdescribed below. The raw materials used are trimethyl gallium (TMGa),trimethyl aluminum (TMAl), trimethyl indium (TMIn), ammonia (NH₃), andsilane (SiH₄). A substrate 71 is prepared. The substrate 71 prepared isa GaN substrate cut at an angle in a range of 0° to 90° toward them-axis out of a (0001) GaN ingot thickly grown by HVPE, with a waferslicing device, in such a manner that the angle ALPHA of tilt of thec-axis toward the m-axis has a desired off angle in a range of 0° to90°. For example, when the substrate is cut at the angle of 75°, theresultant substrate is a {20-21}-plane GaN substrate, and it isrepresented by reference symbol 71 a in the hexagonal crystal latticeshown in part (b) of FIG. 7.

Before the growth, the substrate is observed by the cathodoluminescencemethod in order to check the stacking fault density of the substrate.The cathodoluminescence is to observe an emission process of carriersexcited by an electron beam, and if there is a stacking fault,non-radiative recombination of carriers occurs in the vicinity thereofto be observed as a dark line. The stacking fault density is defined asa density (line density) per unit length of dark lines. Thecathodoluminescence method of nondestructive measurement is appliedherein in order to check the stacking fault density, but it is alsopossible to use a transmission electron microscope of destructivemeasurement. When a cross section of a sample is observed from thea-axis direction with the transmission electron microscope, a defectextending in the m-axis direction from the substrate toward the samplesurface is a stacking fault included in the support base, and the linedensity of stacking faults can be determined in the same manner as inthe case of the cathodoluminescence method.

This substrate 71 is placed on a susceptor in a reaction furnace, andthe epitaxial layers are grown according to the following growthprocedure. First, n-type GaN 72 is grown in the thickness of 1000 nm.Next, an n-type InAlGaN cladding layer 73 is grown in the thickness of1200 nm. Thereafter, an n-type GaN guide layer 74 a and an undoped InGaNguide layer 74 b are grown in the thickness of 200 nm and in thethickness of 65 nm, respectively, and then a three-cycle MQW 75comprising GaN 15 nm thick/InGaN 3 nm thick is grown. Subsequently grownare an undoped InGaN guide layer 76 a in the thickness of 65 nm, ap-type AlGaN block layer 77 in the thickness of 20 nm, and a p-type GaNguide layer 76 b in the thickness of 200 nm. Then a p-type InAlGaNcladding layer 77 is grown in the thickness of 400 nm. Finally, a p-typeGaN contact layer 78 is grown in the thickness of 50 nm.

An insulating film 79 of SiO₂ is deposited on the contact layer 78, andthen photolithography is used to form a stripe window in the width of 10μm by wet etching. In this step, two types of contact windows are formedalong two stripe directions. They are the laser stripe along (1)M-direction (direction of the contact window extending along thepredetermined plane defined by the c-axis and the m-axis), and the laserstripe along (2) A-direction: <11-20> direction.

After the formation of the stripe window, a p-side electrode 80 a ofNi/Au, and a pad electrode of Ti/Al are made by vapor deposition. Next,the back surface of the GaN substrate (GaN wafer) is polished using adiamond slurry to produce a substrate product with the back surface in amirror state. At this time, the thickness of the substrate product ismeasured with a contact film thickness meter. The measurement ofthickness may also be carried out from a sample cross section with amicroscope. The microscope applicable herein is an optical microscope ora scanning electron microscope. An n-side electrode 80 b of Ti/Al/Ti/Auis formed by vapor deposition on the back surface (polished surface) ofthe GaN substrate (GaN wafer).

The cavity mirrors for these two types of laser stripes are producedwith a laser scriber using the YAG laser at the wavelength of 355 nm.When the break is implemented with the laser scriber, the lasing chipyield can be improved as compared with the case using the diamondscribing method. The conditions for formation of the scribed grooves areas follows: laser beam output of 100 mW; scanning speed of 5 mm/s. Thescribed grooves thus formed are, for example, grooves having the lengthof 30 μm, the width of 10 μm, and the depth of 40 μm. The scribedgrooves are formed by applying the laser beam directly to theepitaxially grown surface at the pitch of 800 μm and through theaperture of the insulating film of the substrate. The cavity length is600 μm.

The cavity mirrors are made by fracture using a blade. A laser bar isproduced by break by press against the back side of the substrate. Morespecifically, part (b) of FIG. 7 and part (c) of FIG. 7 show relationsbetween crystal orientations and fractured faces, for the {20-21}-planeGaN substrate. Part (b) of FIG. 7 shows the case where the laser stripeis provided (1) in the M-direction and shows end faces 81 a, 81 b forthe laser cavity along with the semipolar plane 71 a. The end faces 81a, 81 b are approximately perpendicular to the semipolar plane 71 a, butare different from the conventional cleaved facets such as thehitherto-used c-planes, m-planes, or a-planes. Part (c) of FIG. 7 showsthe case where the laser stripe is provided (2) in the <11-20> directionand shows end faces 81 c, 81 d for the laser cavity along with thesemipolar plane 71 a. The end faces 81 c, 81 d are approximatelyperpendicular to the semipolar plane 71 a and are composed of a-planes.

The fractured faces made by the break are observed with a scanningelectron microscope and no prominent unevenness is observed in each of(1) and (2). From this result, the flatness (magnitude of unevenness) ofthe fractured faces is believed to be not more than 20 nm. Furthermore,the perpendicularity of the fractured faces to the surface of the sampleis within a range of ±5°.

The end faces of the laser bar are coated with a dielectric multilayerfilm by vacuum vapor deposition. The dielectric multilayer filmcomprises an alternate stack of SiO₂ and TiO₂. The thickness of eachlayer is adjusted in a range of 50 to 100 nm, and is designed so thatthe center wavelength of reflectance falls within a range of 500 to 530nm. The reflecting surface on one side has ten cycles and the designedvalue of reflectance of about 95%, and the reflecting surface on theother side has six cycles and the designed value of reflectance of about80%.

Evaluation by energization is carried out at room temperature. A powersupply used is a pulsed power source with the pulse width of 500 ns andthe duty ratio of 0.1%, and the energization is implemented with needleson the surface electrodes. On the occasion of light output measurement,the emission from the laser bar end face is detected with a photodiodeto check the current-light output characteristic (I-L characteristic).In measurement of emission wavelength, the emission from the laser barend face is made to pass through an optical fiber, and a spectrumthereof is measured with a spectrum analyzer as a detector. In checkinga polarization state, the emission from the laser bar is made to passthrough a polarizing plate to rotate, thereby checking the polarizationstate. In observation of LED-mode emission, an optical fiber is arrangedon the front surface side of the laser bar to measure light emitted fromthe front surface.

The polarization state after oscillation is checked for every laser, andit is found that the light is polarized in the a-axis direction. Thelasing wavelength is 500-530 nm.

The polarization state in the LED mode (spontaneous emission) ismeasured for every laser. When the polarization component in the a-axisdirection is I1 and the polarization component in the projecteddirection of the m-axis on the principal surface is I2, the polarizationdegree p is defined as (I1−I2)/(I1+I2). In this way, the relationbetween determined polarization degree ρ and minimum of thresholdcurrent density is investigated, and the result obtained is as shown inFIG. 9. It is seen from FIG. 9 that the threshold current densitydemonstrates a significant decrease in the case of the laser (1) withthe laser stripe along the M-direction when the polarization degree ispositive. Namely, it is seen that when the polarization degree ispositive (I1>I2) and when the waveguide is provided along an offdirection, the threshold current density is significantly decreased.

The data shown in FIG. 9 is as described below.

threshold current threshold current polarization degree, (M-directionstripe), (<11-20> stripe), 0.08, 64,  20, 0.05, 18,  42, 0.15, 9, 48,0.276, 7, 52, 0.4, 6

The relation between the tilt angle of the c-axis of the GaN substratetoward the m-axis and lasing yield is investigated, and the resultobtained is as shown in FIG. 10. In the present example, the lasingyield is defined as (the number of lasing chips)/(the number of measuredchips). FIG. 10 is a plot for substrates with the stacking fault densityof substrate of not more than 1×10⁴ (cm⁻¹) and lasers with the laserstripe along (1) the M-direction. It is seen from FIG. 10 that thelasing yield is extremely low with the off angles of not more than 45°.The end face state is observed with an optical microscope, and it isfound that an m-plane appeared in almost all chips, at angles smallerthan 45°, resulting in failure in achieving perpendicularity. It is alsoseen that when the off angle is in a range of not less than 63° and notmore than 80°, the perpendicularity is improved, and the lasing yieldincreases to 50% or more. From these facts, the optimum range of offangle of the GaN substrate is not less than 63° and not more than 80°.The same result is also obtained in a range of not less than 100° andnot more than 117°, which is an angular range to providecrystallographically equivalent end faces.

The data shown in FIG. 10 is as described below.

tilt angle, yield, 10,  0.1, 43,  0.2, 58, 50, 63, 65, 66, 80, 71, 85,75, 80, 79, 75, 85, 45, 90, 35

The relation between stacking fault density and lasing yield isinvestigated, and the result obtained is as shown in FIG. 11. Thedefinition of lasing yield is the same as above. It is seen from FIG. 11that the lasing yield is suddenly decreased with the stacking faultdensity over 1×10⁴ (cm⁻¹). When the end face state is observed with anoptical microscope, it is found that with samples having the decreasedlasing yield, the unevenness of the end faces is significant, and noflat fractured faces are obtained. A conceivable reason is that there isa difference in easiness of fracture because of the existence ofstacking faults. From this result, the stacking fault density in thesubstrate needs to be not more than 1×10⁴ (cm⁻¹).

The data shown in FIG. 11 is as described below.

stacking fault density (cm⁻¹), yield,  500, 80, 1000, 75, 4000, 70,8000, 65, 10000,  20, 50000,   2

The relation between substrate thickness and lasing yield isinvestigated, and the result obtained is as shown in FIG. 12. Thedefinition of lasing yield is the same as above. FIG. 12 is a plot forlasers in which the stacking fault density of the substrate is not morethan 1×10⁴ (cm⁻¹) and in which the laser stripe extends along (1) theM-direction. From FIG. 12, the lasing yield is high when the substratethickness is not more than 100 μm and not less than 50 μm. This isbecause the perpendicularity of fractured faces becomes deterioratedwhen the substrate thickness is larger than 100 μm. It is also becausehandling becomes difficult and a chip becomes easy to break when thethickness is smaller than 50 μm. From these, the optimum thickness ofthe substrate is not less than 50 μm and not more than 100 μm.

The data shown in FIG. 12 is as described below.

substrate thickness, yield,  48, 10,  80, 65,  90, 70, 110, 45, 150, 48,200, 30, 400, 20 

Example 3

The substrate used is a {20-21}-plane GaN substrate grown by HVPE, andan n-type GaN layer is grown in the thickness of 1000 nm on this GaNsubstrate. A scribed groove is formed in the GaN-based semiconductorgrown in this way, by laser scribing. The size of a damaged regionformed around the scribed groove is investigated. The scribed groove isformed with a laser scriber using the YAG laser at the wavelength of 355nm. The processing conditions are as follows. Laser beam output 100 mw;scanning speed 5 mm/s.

The scribed groove thus formed is a groove having approximately thelength of 200 μm, the width of 10 μm, and the depth of 40 μm.

In the present example, the damaged region is evaluated by thecathodoluminescence method. The cathodoluminescence is to observe anemission process of carriers excited with an electron beam. However, ifprocessing damage or the like is introduced by formation of the scribedgroove, non-radiative recombination centers are formed near the regionwhere the scribed groove is formed. For this reason, carriers undergonon-radiative recombination in the damaged region, and therefore thedamaged region is observed as a dark region. Since the diffusion lengthof carriers in GaN is about 0.1 μm, the damaged region of several μmorder can be observed. Since an increase in acceleration voltage resultsin increasing information about the interior of crystal, the observationis carried out using a relatively low acceleration voltage of not morethan 10 kV to observe a surface layer region of not more than 0.5 μmfrom the surface, whereby an abnormal region with great damage can bediscriminated from a normal region. FIG. 13 shows an example of acathodoluminescence (CL) image showing the region around the scribedgroove. FIG. 14 is an example of a scanning electron microscope (SEM)image showing the region around the scribed groove. Dark and lightregions are observed near the scribed groove, not only in the CL imagebut also in the SEM image.

The scribed groove shown in FIGS. 13 and 14 is formed by a scan in adirection of arrow A with a laser beam. The laser scans from the leftend in these drawings to start forming the scribed groove, and the laserirradiation is terminated at the right end. In a certain period (initialperiod) from the time of the start, the laser power is continuouslyincreased. In a period (end period) from a time a little before the endto the time of the end, the laser power is continuously decreased. In aperiod between the initial period and the end period, the laser power isnot intentionally changed. By this laser power control, the groove isformed in the shape shown in the cross-sectional image of FIG. 15 (e.g.,the shape of a ship bottom). The groove shape shown in FIG. 15 enablesformation of the fractured face suitable for the cavity. Thecross-sectional shape of the scribed groove has the bottom shape of aboat (ship).

It is shown in the cross-sectional image of FIG. 15 that the scribedgroove and scribed mark include a first slope portion formed in the endperiod of the scribing, a second slope portion formed in the initialperiod of the scribing, and a flat portion between the first slopeportion and the second slope portion. The length of the second slopeportion (initial end) is shorter than the length of the first slopeportion (terminal end). The tilt of the bottom in the first slopeportion (terminal end) is gentler than the tilt of the bottom in thesecond slope portion (initial end). A tilt angle AG2 between a straightline connecting a start point and an end point in the second slopeportion (initial end) and a straight line extending along theepitaxially grown surface is larger than a tilt angle AG1 between astraight line connecting a start point and an end point in the firstslope portion (terminal end) and the straight line extending along theepitaxially grown surface. An angle BG2 between the straight lineconnecting the start point and the end point in the second slope portion(initial end) and the epitaxially grown surface is smaller than an angleBG1 between the straight line connecting the start point and the endpoint in the first slope portion (terminal end) and the epitaxiallygrown surface.

Part (a) of FIG. 15 shows the CL image of the scribed mark remainingnear the edge of the fractured face. The CL image is the result ofobservation of an emission image, and the dark-contrast region in the CLimage includes a large number of non-radiative centers formed by thelaser irradiation. Part (b) of FIG. 15 shows the SEM image of thescribed mark remaining near the edge of the fractured face. The SEMimage is the result of observation of an image by secondary electrons,and the dark region in the SEM image includes a large number of alteredportions made by the laser irradiation.

Referring again to FIGS. 13 and 14, the length of the scribed groove is200 μm with reference to the SEM image. With reference to the CL image,the emission is weak in a region of about 30 μm from the start portionof the scribed groove, and this indicates that damage is introduced tothis region. On the other hand, in the end portion of the scribedgroove, the damaged region in the CL image is approximately the same asthe terminal end position of the scribed groove, and this indicates thatthe damaged region is not more than several μm of the end portion. It isshown with reference to the SEM image that a large number of debris(deposits made by ablation) exist in the damaged region. However, thereis few debris on the right side of the terminal end of the scribedgroove. This suggests that the end portion of laser irradiation may becloser than 70 μm to the waveguide, without degradation of the lasercharacteristic. More specifically, the end of the scribed groove can belocated close to the laser stripe in a range of not less than 20 μm andless than 70 μm. This allows the gap between scribed grooves to bedecreased. Since the decrease in the gap between scribed grooves allowsimprovement in perpendicularity upon fracture and decrease in chipwidth, it can increase the number of chips taken out of one wafer.Therefore, it is feasible to increase the yield in formation of thefractured face and increase the number of chips taken. As a result ofthis, it is feasible to decrease production cost.

Since the evaluation is conducted by the cathodoluminescence method asdescribed above, the cathodoluminescence allows observation of theemission process of carriers excited with an electron beam. Whenprocessing damage or the like is introduced during formation of thescribed groove, carriers undergo non-radiative recombination in thevicinity of the damaged region. Because of the carrier recombination atnon-radiative centers, the damaged region is observed as a dark region.Since the diffusion length of carriers in GaN is about 0.1 μm, it isfeasible to observe the damaged region of several μm order. The depth ofobservation is preferably deeper than the scribed groove, but increasein acceleration voltage results in increasing information about theinterior of crystal. Therefore, the observation is preferably carriedout using a relatively low acceleration voltage of about not more than10 kV and not less than 3 kV. The use of such acceleration voltageallows the information about carrier recombination centers from thesurface layer to be obtained as a visual image.

From the above description, an estimation can be made about a level ofdamage around a groove by making use of the method for evaluating thedamage caused by formation of the scribed groove. By this method, thereappears a difference according to damage due to formation of the scribedgroove in the image of the region near the groove, which is obtainedwith a scanning electron microscope, a cathodoluminescence measuringdevice, or the like. The estimation can be made about the level ofdamage to an adjacent region to the groove, based on the image with thescanning electron microscope or the cathodoluminescence measuringdevice.

The method for evaluating the damage can include, for example, thefollowing steps shown in FIG. 16. Step S201 is to prepare asemiconductor device to be subjected to processing of a groove. Thesemiconductor device can include a substrate comprising a hexagonalIII-nitride semiconductor and a hexagonal III-nitride semiconductorregion formed on the substrate, or can include a substrate comprising ahexagonal III-nitride semiconductor. Step S202 is to form a groove inthe semiconductor device including the hexagonal III-nitridesemiconductor, using a device for forming a scribed groove. Step S203 isto obtain an image of an area including the groove of the semiconductordevice, using either of the scanning electron microscope and thecathodoluminescence measuring device for the semiconductor device, afterthe formation of the groove. Step S204 is to make an estimation about alevel of damage to the area near the groove, based on the image. StepS205 is to determine the distance between the end of the scribed grooveand the laser stripe of the semiconductor laser and/or a formingcondition of the scribed groove. Step S206 is to form a substrateproduct for III-nitride semiconductor laser device. Step S207 is to formthe scribed groove in the substrate product, using the determinedforming condition and groove distance. Step S208 is to perform breakupof the substrate product by press on the substrate product, after theformation of scribed groove in the substrate product. This breakupresults in, for example, obtaining a laser bar and/or a laser chip.

Example 4

FIG. 17 is a list of dimensions of scribed grooves in an experimentconducted for obtaining the chip widths of 200 μm, 150 μm, and 100 μm.FIG. 18 is a drawing showing an arrangement of scribed grooves SG andlaser stripes LS. The end-side space corresponds to the distance W1 andthe start-side space to the distance W2. On the start side, a space of30 μm to the waveguide is necessary in order to avoid damage. On the endside, a space of 10 μm is necessary because of a problem of positionalaccuracy. Therefore, the minimum groove pitch is 40 μm. Unless thebottom surface of the scribed groove is the ship bottom shape,repeatability of groove depth becomes worse, and thus the minimum groovelength is 40 μm. The “margin of +α” means a room for minimizing theadverse effect of debris. In fabrication of devices with the chip width,for example, of 100 μm-200 μm, the dimensional ranges of the shape ofthe scribed groove are estimated as described below.

chip width, length of scribed groove, scribed groove pitch, 200 μm, 40μm-160 μm, 160-40 μm, 150 μm, 40 μm-110 μm, 110-40 μm, 200 μm, 40 μm-60μm,  60-40 μmIn this estimation the minimum length of the scribed groove is 40 μm.When the length of the scribed groove is not less than 40 μm, thefractured face has sufficient perpendicularity.

Example 5

A laser diode is grown by metal-organic vapor phase epitaxy as follows.The raw materials used herein are trimethyl gallium (TMGa), trimethylaluminum (TMAl), trimethyl indium (TMIn), ammonia (NH₃), and silane(SiH₄). The substrate used is a {20-21}-plane GaN substrate grown byHVPE.

This substrate is placed on a susceptor in a reaction furnace, andepitaxial layers are grown according to the following growth procedure.First, an n-type GaN layer is grown in the thickness of 1000 nm. Next,an n-type InAlGaN cladding layer is grown in the thickness of 1200 nm onthe n-type GaN layer. Subsequently, an n-type GaN guide layer and ann-type InGaN guide layer are grown in the thickness of 250 nm and in thethickness of 115 nm, respectively, and thereafter a two-cycle MQW isgrown in the configuration of GaN barrier layers (10 nm thick)/InGaNwell layers (3 nm thick). Then grown are an undoped InGaN guide layer inthe thickness of 65 nm, a p-type AlGaN block layer in the thickness of20 nm, a p-type InGaN guide layer in the thickness of 50 nm, and ap-type GaN guide layer in the thickness of 250 nm. Next, a p-typeInAlGaN cladding layer is grown in the thickness of 400 nm. Finally, ap-type GaN contact layer is grown in the thickness of 50 nm. Anepitaxial substrate is produced through the procedure of these steps.

An insulating film of SiO₂ is deposited on the contact layer, andthereafter, the photolithography is used to form a stripe window in thewidth of 10 μm by wet etching. The laser stripe is provided in parallelwith the projected direction of the c-axis on the principal surface. Theangle between the waveguide vector and the c-axis vector is not morethan 0.1°. After formation of the stripe window, a p-side electrode ofNi/Au and a pad electrode of Ti/Au are deposited by vapor deposition.Thereafter, the back surface of the GaN substrate (GaN wafer) ispolished using diamond slurry to produce a substrate product with theback surface in a mirror state. An n-side electrode of Ti/Al/Ti/Au isformed by vapor deposition on the back surface (polished surface) of theGaN substrate (GaN wafer). The substrate product for the gain guidingtype laser shown in FIG. 19 can be fabricated according to the procedureof these steps.

It is also possible to fabricate an index guided laser with the ridgestructure shown in FIG. 20, by the following method. For producing theridge structure in the width of 2 μm, a mask of a positive resist with apattern in the width of 2 μm is provided by photolithography. The laserwaveguide is directed so as to be parallel to the direction of theprojected component as a projection of the c-axis vector on theprincipal surface. The ridge structure is produced by dry etching usingCl₂. The etching depth is, for example, 0.7 μm, and the etching of thesemiconductor region of the epitaxial substrate is carried on until theAlGaN block layer becomes exposed. After the etching, the resist mask isremoved. The stripe mask in the width of about 2 μm is left on the ridgestructure by photolithography. The direction of the stripe mask isaligned with the direction of the ridge structure. After this, SiO₂ isdeposited by vacuum vapor deposition on the side faces of the ridge.After the vapor deposition of the insulating film, SiO₂ on the ridge isremoved by the lift-off method to form the insulating film with thestriped aperture. Next, an anode electrode AND2 and a cathode electrodeCTD2 are formed to obtain the substrate product. The scribed grooves tobe formed in a subsequent step are also depicted in FIGS. 19 and 20.

The cavity mirrors for these laser stripes are produced with a laserscriber using the YAG laser at the wavelength of 355 nm. The lasing chipyield can be higher in the case where the scribed grooves are formedwith the laser scriber, followed by break, than in the case using thediamond scribing method. The conditions for formation of the scribedgrooves are as follows.

Laser beam output: 100 mW.

Scan speed: 5 mm/s.

The scribed grooves thus formed are grooves, for example, having thelength of 100 μm, the width of 10 μm, and the depth of 40 μm. In theformation of scribed grooves, the laser scriber is controlled so thatthe groove pitch becomes 50-300 μm, and the laser scriber is controlledso that the distances between the scribed groove ends and the waveguidebecome in a range of 10 to 300 μm. The scribed grooves are periodicallyformed by direct irradiation with the laser beam through the aperture ofthe electrode to the surface of the substrate. The cavity length is 600μm. The definitions of the distances W1, W2 are shown in FIGS. 19 and 20as described above.

A blade is used to press against the back surface of the substrate toproduce the cavity mirrors by fracture. A laser bar is produced bybreaking the substrate by press at the end on the back side of thesubstrate. The method of using as the mirror surfaces the end facesperpendicular to the waveguide provided in parallel with the projecteddirection of the c-axis on the semipolar principal surface is differentfrom the conventional cleaved facets such as m-planes, a-planes, orc-planes which are used as the end faces in lasers such as theconventional c-planes or m-planes. A scribed groove (with the groovelength of 100 μm and the groove pitch of 300 μm) in the laser bar isobserved from a cross section thereof. There is no contrast observed ineither of a secondary electron image (SE image) and a CL image, at theterminal end of the scribed groove. On the other hand, there is acontrast observed in the secondary electron image of the start portionof the scribed groove, and it is shown that the semiconductor regionnear the scribed groove is altered in a level to change the secondaryelectron emission rate. There is also a contrast seen in the CL image,and the altered region in the SE image is observed as a non-radiativeregion.

The end faces of the laser bar thus produced are coated with adielectric multilayer film by vacuum vapor deposition. The dielectricmultilayer film is composed of an alternate stack of SiO₂ and TiO₂. Thethickness of each layer is adjusted in a range of 50-100 nm and designedso that the center wavelength of reflectance falls within a range of500-530 nm. The reflecting surface on one side consisted of ten cyclesand the designed value of reflectance is about 95%. The reflectingsurface on the other side consisted of six cycles and the designed valueof reflectance is about 80%.

Evaluation by energization is conducted at room temperature. A powersupply used is a pulsed power supply with the pulse width of 500 ns andthe duty ratio of 0.1%, and the energization is conducted with needleson the surface electrodes. In measurement of optical output, theemission from the end face of the laser bar is detected with aphotodiode to check the current-optical output characteristic (I-Lcharacteristic). In measurement of emission wavelength, the emissionfrom the end face of the laser bar is made to pass through an opticalfiber, and a spectrum thereof is measured with a spectrum analyzer as adetector. The lasing wavelength is 500-530 mm.

An investigation is carried out to investigate dependence of lasingyield on the distances between the waveguide and grooves. FIG. 21 showsthe dependence of lasing yield on the distances between the waveguideand the scribed grooves. The relative threshold current density on thevertical axis is defined by an increase rate from an intermediate valueof oscillation threshold current density in a hundred chips of laserdevices. A characteristic curve CS represents a relation of the distancebetween the start end of the scribed groove and the waveguide versuslasing yield, and a characteristic curve CE represents a relation of thedistance between the terminal end of the scribed groove and thewaveguide versus lasing yield. With reference to FIG. 21, when theterminal end is made closer to the waveguide and when the distance W1 isnot less than 20 μm, the lasing yield is improved, without degradationof the laser characteristic. On the other hand, when the start end ismade closer to the waveguide and when the distance W2 is not less than50 μm, the lasing yield becomes deteriorated with degradation of thecharacteristic. From this result, the terminal end with little damagecan be located closer up to the distance of not more than 70 μm from thewaveguide, and the distance can be not less than 20 μm. This allowsreduction in chip width. For this reason, the number of chips takenincreases, so as to reduce cost.

Example 6

In Example 2, the plurality of epitaxial films for the semiconductorlaser is grown on the GaN substrate having the {20-21} plane. The endfaces for the optical cavity are formed by the formation of scribedgrooves and the press as described above. In order to find candidatesfor these end faces, plane orientations making an angle near 90° to the(20-21) plane and being different from the a-plane are determined bycalculation. With reference to FIG. 22, the following angles and planeorientations have angles near 90° to the (20-21) plane.

specific plane index, angle to {20-21} plane, (−1016), 92.46°, (−1017),90.10°, (−1018), 88.29° 

FIG. 23 is a drawing showing atomic arrangements in the (20-21) plane,(−101-6) plane, and (−1016) plane. FIG. 24 is a drawing showing atomicarrangements in the (20-21) plane, (−101-7) plane, and (−1017) plane.FIG. 25 is a drawing showing atomic arrangements in the (20-21) plane,(−101-8) plane, and (−1018) plane. As shown in FIGS. 23 to 25, localatom arrangements indicated by arrows show configurations of neutralatoms in terms of charge, and electrically neutral atom arrangementsappear periodically. The reason why the relatively normal faces areobtained to the grown surface can be that generation of fractured facesis considered to be relatively stable because of the periodic appearanceof the neutral atomic configurations in terms of charge.

According to various experiments including the above-described Examples1 to 6, the angle ALPHA can be in a range of not less than 45° and notmore than 80° or in a range of not less than 100° and not more than135°. In order to improve the lasing chip yield, the angle ALPHA can bein a range of not less than 63° and not more than 80° or in a range ofnot less than 100° and not more than 117°. The typical semipolarprincipal surface can be any one of the {20-21} plane, {10-11} plane,{20-2-1} plane, and {10-1-1} plane. Furthermore, the principal surfacecan be a slight slant surface from these semipolar planes. For example,the semipolar principal surface can be a slight slant surface off in arange of not less than −4° and not more than +4° toward the m-plane fromany one of the {20-21} plane, {10-11} plane, {20-2-1} plane, and{10-1-1} plane.

As described above, the embodiment provides a III-nitride semiconductorlaser device with a laser cavity enabling a low threshold current, on asemipolar plane of a support base tilting from the c-axis toward them-axis of a hexagonal III-nitride. The embodiment provides a method forfabricating the III-nitride semiconductor laser device. The embodimentprovides a method for estimating damage from formation of a scribegroove in a semiconductor laser device.

Described and illustrated the principle of the invention in a preferredembodiment thereof, it is appreciated by those having skill in the artthat the invention can be modified in arrangement and detail withoutdeparting from such principles. Although a light emitting device isdescribed for illustrative purposes in the embodiments, a p-sideelectrode of electronic devices such as transistors and diodes is alsoavailable. We therefore claim all modifications and variations comingwithin the spirit and scope of the following claims.

1. A method of fabricating group-III nitride semiconductor laser device,the method comprising the steps of: preparing a substrate comprising ahexagonal group-III nitride semiconductor and having a semipolarprincipal surface; forming a substrate product having a laser structure,an anode electrode, and a cathode electrode, the laser structureincluding a semiconductor region and the substrate, the semiconductorregion being formed on the semipolar principal surface; scribing a firstsurface of the substrate product in a direction of an a-axis of thehexagonal group-III nitride semiconductor to form first and secondscribed grooves; and carrying out breakup of the substrate product bypress against a second surface of the substrate product, to form anothersubstrate product and a laser bar, wherein the first surface is asurface opposite to the second surface, wherein the semiconductor regionis located between the first surface and the substrate, wherein thelaser bar has first and second end faces extending from the firstsurface to the second surface and made by the breakup, wherein the firstand second end faces form a laser cavity of the group-III nitridesemiconductor laser device, wherein the anode electrode and the cathodeelectrode are formed on the laser structure, wherein the semiconductorregion includes a first cladding layer comprising a first conductivitytype GaN-based semiconductor, a second cladding layer comprising asecond conductivity type GaN-based semiconductor, and an active layerbeing provided between the first cladding layer and the second claddinglayer, wherein the first cladding layer, the second cladding layer, andthe active layer are arranged along a normal axis to the semipolarprincipal surface, wherein the active layer includes a GaN-basedsemiconductor layer, wherein a c-axis of the hexagonal group-III nitridesemiconductor of the substrate tilts at an angle ALPHA with respect tothe normal axis toward an m-axis of the hexagonal group-III nitridesemiconductor, wherein the first and second end faces intersect with anm-n plane defined by the m-axis of the hexagonal group-III nitridesemiconductor and the normal axis, wherein the angle ALPHA is in a rangeof not less than 45° and not more than 80° or in a range of not lessthan 100° and not more than 135°, wherein the substrate product includesa laser stripe extending above the semipolar principal surface, whereinthe laser stripe extends in a direction of a waveguide axis, wherein thewaveguide axis extends from one to the other of the first and second endfaces, wherein the first scribed groove, one of the laser stripes, andthe second scribed groove are arranged in order in a direction of thea-axis of the hexagonal group-III nitride semiconductor, wherein thefirst scribed groove has an end formed on the first surface, wherein thesecond scribed groove has an end formed on the first surface, wherein afirst distance between the laser stripe and the end of the first scribedgroove is smaller than a second distance between the laser stripe andthe end of the second scribed groove, and wherein a distance between theend of the first scribed groove and the end of the second scribed grooveis smaller than a width of the group-III nitride semiconductor laserdevice.
 2. The method according to claim 1, wherein the first and secondscribed grooves are provided along a predetermined a-n plane defined bythe a-axis of the hexagonal group-III nitride semiconductor and thenormal axis.
 3. The method according to claim 1, wherein the firstdistance is not less than 20 μm and less than 50 μm.
 4. The methodaccording to claim 1, wherein the first distance is less than 50 μm, andwherein the second distance is not less than 50 μm.
 5. The methodaccording to claim 1, wherein a width of the group-III nitridesemiconductor laser device is not more than 200 μm.
 6. The methodaccording to claim 1, wherein an end face of the active layer in each ofthe first and second end faces makes an angle in a range of not lessthan (ALPHA−5)° and not more than (ALPHA+5)° on a plane defined by thec-axis and the m-axis of the hexagonal group-III nitride semiconductor,with respect to a reference plane perpendicular to the m-axis of thesupport base comprising the hexagonal nitride semiconductor.
 7. Themethod according to claim 1, wherein the angle ALPHA falls within arange of not less than 63° and not more than 80° or within a range ofnot less than 100° and not more than 117°.
 8. The method according toclaim 1, wherein the step of forming the substrate product comprisesperforming processing such as slicing or grinding of the substrate sothat a thickness of the substrate becomes not more than 400 μm, thesecond surface being a processed surface made by the processing or asurface including an electrode formed on the processed surface.
 9. Themethod according to claim 1, wherein the step of forming the substrateproduct comprises polishing the substrate so that the thickness of thesubstrate becomes not less than 50 μm and not more than 100 μm, thesecond surface being a polished surface formed by the polishing or asurface including an electrode formed on the polished surface.
 10. Themethod according to claim 1, wherein the scribing is carried out using alaser scriber.
 11. The method according to claim 1, wherein thesemipolar principal surface is one of a {20-21} plane, a {10-11} plane,a {20-2-1} plane, and a {10-1-1} plane.
 12. The method according toclaim 1, wherein the laser structure further comprises an insulatingfilm with an aperture, the insulating film being provided on thesemiconductor region, wherein the electrode is connected through theaperture of the insulating film to the semiconductor region of the laserstructure, wherein the first distance is defined by a distance betweenthe aperture of the insulating film and the end of the first scribedgroove, and wherein the second distance is defined by a distance betweenthe aperture of the insulating film and the end of the second scribedgroove.
 13. The method according to claim 1, wherein the semiconductorregion of the laser structure has a ridge structure, wherein the firstdistance is defined by a distance between the ridge structure and theend of the first scribed groove, and wherein the second distance isdefined by a distance between the ridge structure and the end of thesecond scribed groove.